I have recognized this also earlier, but after witnessing it now in WoW, it appears even more obvious: part of the so-called addiction tendency into MMORPGs must be related to its share of people with a certain personality type: one which is has traits of strong sense of responsibility, need for closure in whatever undertaking one becomes engaged with, and related hard-working and thorough behaviour patterns, concluding easily into major investment of time and effort. For some people it just appears very hard to step down from a quest once started: and a game like WoW is built around the principle of endless network of overlapping, always-incomplete quest structure which just goes on. (Signed by: “Running errands around Dun Morogh until six am”)
frans goes blog 
It’s 00:00 here and I just finished 4 fedex style quests in WoW. I should be in bed, I said I’d go when I did hte four. But then 1 of them led to a new one.
Arg.