Oh goodness, yes, I've played Everquest and several other MMORPGs (Massively Multiplayer Online Role Playing Games) over the years. And yes, I can unabashedly say I'm probably addicted to them.
I went from Everquest (EQ) to Dark Age of Camelot (DAoC), to City of Heroes (CoH), to City of Villains (CoV), to Everquest 2 (EQ2), to World of Warcraft (WOW), back to DAoC.
My passion for the gaming industry actually led to landing a job working for one of the companies that makes them, and I was there for just under 5 years.
It definitely IS easy to lose yourself in those kinds of games, if you're not careful, and you have to remind yourself that there's a life outside the computer sometimes!
Personally, I agree with the sentiment that an addiction to an online game is one of the more harmless addictions out there... assuming, of course, that you don't let it take over your life, where you find yourself ignoring your friends, family, loved ones, etc. When that starts to happen, then yeah, it's a problem.
I'm bad, though... I try to recruit my friends to play my games with me, that way, I'm not ignoring them!
Online games can be a good thing, too, though. By the nature of it being "Massively Multiplayer", there are several thousand people playing the same game, at the same time, and you can easily find yourself making new friends. It's like one big instant messaging system with pretty graphics, monsters and heroes!
In all seriousness, though, I'm made some really great "real life" friendships through my online gaming experiences. Plus, these games are a great way to live out your inner child's make-believe fantasies. For the typical $15 or so a month, I say that's pretty cheap entertainment, for the amount of entertainment I get out of them.
