One of the reasons I've continued to subscribe to WoW is I've always managed to keep it balanced.
Sticking to one main character - my hunter - helps with that, because if I don't invest time in playing other characters I don't end up playing as much overall.
The past couple of weeks, two different friends have been playing WoW; one a fairly new player who I felt obliged to help out (because I'd been trying to get him to play for years), and one a raiding veteran in a small horde guild that needed another member for raids.
Feeling pressured to play not one, but two alts as well as my hunter was getting to me. It seems stupid that a game would stress you out, but it does happen.... and I think the stress filtered through into real life, where I made decisions (totally unrelated to WoW, incidentally) that I might not have made otherwise.
I don't think I'd change anything - although the newbie will almost certainly never play again and I haven't decided whether to try and raid on my druid or not - but it's a lesson I will keep in mind for next time.