Well, i've playing wow since late '05, I've only been in low level instances (Deadmines etc.) my highest level char is 65 or so, i've been part of 2 guilds, none were active in instances, and only mildly so in PvP.
And as such, I haven't been on wow for more than 30mins since i got GTA IV, I don't have any in game commitments that mean i have to be there at a certain time, I'm not going to miss any important guild news so it doesn't matter if i'm there or not.
For me when i was playing TFC with a clan, the biggest thing was having to be online and ready to go for the practice session before the clan match, then onto the main event, I didn't realise with practice every evening, and a clan match at least once a week it was taking up ALL my free time... Really not worth it.
The trick is to not get heavily involved in groups of players who take the game super seriously, go find a casual guild, avoid things that require you to be online and in a certain area at a set time and you'll be set
As to playing with people you know, make it clear that you're only playing when you want to, and if a run is going to take X hours, tell them to have fun and go off and do something else, even if it means spending time with people in the real world
