For various reasons World of Warcraft's dungeon finder system is now in many ways the heart of their game.
It's a significant part of most people's leveling experience. You don't need to level with it but most people use it either to break up the routine of questing or as a priority while leveling. In a culture where players famously always find the shortest path to the cheese the dungeon finder gives the best experience and items for the time invested.
It's essential for gearing up for raiding when you reach 85. Later in the expansion it might be possible to skip straight to raids when you ding but that's not the case at the moment unless you raid with people who don't mind blatantly carrying you.
It's likely to be a side pursuit of even the most active raiders. Whether people are supplementing their conquest points with daily heroics, collecting justice points (which will become more useful in due course as we will be able to buy trade resources with them) or altruistically helping guildies even people who are regularly doing raiding are likely to run heroics, at least once per day.
It ties in to non-standard pursuits too like the collection of achievement points and mounts. It's highly accessible compared to raids and is available at any hour of the day with very little commitment (as no one bats an eyelid about bailing on their group if it suits them to do so).
Thus for many players LFD is the game. Daily quests, auction house trading and so on are just supplementing their main game which is running 5 man dungeons.
Also nearly everyone uses the random dungeons rather than choose a specific dungeon they particularly want. You gain a 5% stat boost, get bonus Justice Points (or once per day Conquest Points), and bonus gold while still being able to make your team up of what friends you have available. You can even queue with 5 pre-selected people.
The Dungeon Finder also ties in with the new guild experience system awarding guild reputation for doing dungeons as a guild group which unlocks a number of special item rewards.
All in all LFD is very heavily incentivised and is likely to be more or less worth doing for the lifetime of the expansion. (Later on the rewards might be less thrilling but people will over-gear these instances).
It's also generally a good experience. WoW's impatient and rather rude community means people are very careful never to do anything that might attract criticism. So the plus side of this type of community is that people are careful to be competent. No one wants to be shouted at as the noob who didn't do the right dance step at the right time. So groups are efficient.
Of course when it's not a good experience it can be very annoying. People are lightning fast to point fingers at anyone but them and are brutally frank about your perceived failings. They are quite often wrong although it's not nice to be called a retard and a noob even if you did make a mistake. Sometimes you don't even need to do anything before people start telling you what's wrong with you. Just zoning in is taken as a request for abuse.
There are workarounds including clicking away from the chat so they can rant all they like but you just don't see it, not talking, playing with at least some friends - ideally on voice comms - so you can just laugh off these insane rants or going with the flow and getting your elitism in first (establishing someone else as the person the bullies should be picking on is a tried and tested defence mechanism). Other options include simply being too thick-skinned to care what rude random strangers on the internet have to say (which is sensible) or trolling them (which can be entertaining).
But in any event the vast majority of people are inoffensive and even civil with occasional moments where you meet people you really like (but have no mechanism of playing with again).
It feels that the system is better than EQ2's mentoring. I lost interest in EQ2 because I really got stuck in the Doldrums around level 60. Miles off end game, too low for my friends to get anything for themselves when they group with me, too high to get easy groups with strangers. I was playing with a friend I've known for years but the problem with these games is the loot cycle gets under your skin. In a sense it would have made sense for him to drop down to play with me even though there would be no loot. Because I got bored of being on my own then he got bored of being on his own after his high level mates formed a clique for which he was not needed. We probably would still be there had we both had each other for company. Now that's not a dig at my mate, I might have done the same had the positions been reversed. My point is that these games are about progression and it's very tedious to stall your progress, you become addicted to the next upgrade. And that's why mentoring doesn't really cut it compared to Dungeon Finder - because people would rather do stuff that upgrades them with random strangers than mark time with friends.
So LFD is the future of dungeon running in all diku mmos I think. It may take some time for the others to realise it and figure out how to implement it; there may be some reservations about the effects on communities as ties of server and guild get replaced by greater internet fuckwads but for the majority being able to maintain the flow of shinies whenever we want outweighs the problem of dealing with rude or bad players.
I think what we will see is tuning of the system to allow greater control over who gets into your groups. Melmoth proposed an excellent solution to this here. I think something like this is inevitable - the if you like this you may also like these technology is so pervasive on the internet and it's clearly needed for LFD systems. It's not necessarily that I trust my friends of friends' friends to be sound judges of character, it's the idea that people are anonymously judging you and rating you that will have a big impact in keeping people civil.
Incidentally good manners correlate quite closely to the danger of violence. Medieval chivalry developed out of a need to have a social structure where wandering knights could meet each other without killing each other. In Japanese culture people were and are extraordinarily careful not to give offence, often bowing several times for the most trivial of reasons. This is because the mediaeval samurai had a right of "cutting and going away" - the right to kill any commoner for any perceived slight. If you want to get good manners on the internet there must be a perception that other people can do damage. Not physical damage for obvious reasons but damage to one's reputation.
I think until then WoW's going to be something of a mixed bag. I've enjoyed playing it for the last 7 weeks but I'm also quite looking forward to moving on to another game where people behave better. It's not that LFD runs aren't good experiences, they usually are. But it's that almost everyone is terrified of showing any individuality in case they get into an argument and get kicked. People are scared to be non-cookie cutter, scared to talk, scared to make mistakes - I'd rather play games with people who are a bit more exuberant.