I'll add my perspective to this as someone who was addicted to a similar game.
I started playing Everquest (EQ) soon after launch in 1999 and leveled pretty quickly hitting the max level cap at the time (50) not long before the first expansion came out. At the time played wi an American guild (I'm Australian) and the time difference stopped me doing things with them most of them time since I had a 9-5 job. My server split and I went with them. The new server was fairly desolate and I ended up getting booted from lack of participation. That, combined with how my class had been screwed by the expansion, caused me to quit.
But I ended up selling my stuff on eBay for ~$3500 so it wasn't all bad. But the story doesn't end there.
Atually anoeth factor was that I was moving to the UK for work. That first year the was one of the most productive of my life. I had no Internet access at home (2001), no TV and a fairly active social life. Due to living in a cheap area of London, renting a flat and subletting the rooms and the low rate of effective taxation of contractors I SAVED in excess of $100,000 that year.
After some drama with flatmates (subletting was financially beneficial but a hassle) I moved closer to work. Suddenlyinsread of an our commute each way I had a 5 minute walk. I got cable Internet and bought a PC and a TV.
I started playing EQ again. New server, new class, starting from scratch. I leveled quickly and went through a series of guilds. Raiding can be a huge timesink. This period was the most fun I had in an MMORPG ever.
Later that year I got laid off as in the aftermath of the telco bubble bursting the previous year (it was 2002 by now).
I'd always wanted to learn a foreign language soi moved to Germany and enrolled in intensive learning classes.
But I still kept up with EQ. I transferred servers to a high end guild. The guild was American so I ended up sleeping from 7pm to 1am, playing EQ from 1am to 8am, going to classes til 1pm and then playing til 6pm. I never really adjusted to sleeping at these times.
But I did go to classes. After they ended I stayed and was playing up to 16 hours a day. In the end I got kicked from the guild for doing something I shouldn't have, which was probably the best thing that could've happened.
Still I view that time now as a wasted opportunity. I did learn the language but not as well as I could have and I certainly take full advantage socially or even to see and do things there.
But not before I'd gone back to my old company (they were hiring again) and my weird schedule had brought me into conflict with a toxic project manager, ending that job only a month after it had started.
2002-03 was a pretty terrible time in the UK contractor market (39% unemployment amongst those who hadn't left the industry). It took months to find a new job. I'd also lost that "social" outlet of EQ so was pretty cut off. It was actually a fairly dark period for me.
I have played MMOGs since then but never to the same intensity and, frankly, I think the magic was gone. I'd seen it all before. Even now I think all these games are fairly formulaic with the same basic mechanics and psychological devices (compulsion loops, etc).
What I learnt about myself is that I'm fairly singleminded. This can be used advantageously as I'll dwel on a problem at work until I solve it. But if I have an unresolved issue personally it can, in a way, consume me--or at least consume my attention.
I do think I'd be better off without a TV or even without a home Internet connection. But I guess balance is my personal cross to bear.
Are these games dangerous? Possibly but I tend to thinkpretty much everything is dangerous to some people. Alcohol. Gambling. Trading. Even working out. It ultimately comes down to personal responsibility.
EDIT: One last thing I'll add: one problem with this kind of game is the longevity (timesink) nature. You see a similar (but much less severe) problem with tabletop RPGs. Because you invest so much time it increases your threshold for putting up with crap, basically.
In RPGs it might be a 7 hour session where nothing happens. In MMOGs it's spending 1-2 hours LFG (looking for group), a week figuring out a raid encounter, spending an our doing a CR (corpse recovery) and so on.
These days my leisure gaming activities are dominated by tabletop board gaming of the Euro variety (Agricola, Age of Steam, Reef Encounter, Le Havre, Dominion and so on). These tend to last 2-3 hours tops and, as such, have very little "downtime". I find it a much more rewarding experience than huge timesink games of any variety. Plus it's actually social.
On a side note, if there is anyone in NYC with interest I playing such games, contact me via my info. :)
EDIT2: fixed some typos (typing on an iPad is error-prone), :)