Two weekends back, a bonus weekend got me back into Runes of Magic for the first time in a while - I've since gained ten levels in both of my two classes. This week, SOE's winback double exp week has gotten me back into EQ2, where I've gained 12 AA's and counting, with an evening left to go. (There hasn't been any announcement, but SOE often opens up bonus exp on holiday weekends as well, so next weekend is a possibility.)
As an MMO tourist, I'm probably amongst those players most likely to wander back to a game for this type of event - for most of the regular residents, these things provide an occasion to perhaps put in a little extra time, but probably not any significant purchasing decisions. Still, I suppose it's a good thing overall. Perhaps a bit of extra money for the developers, and otherwise just a little something for everyone else to remember.
I'd write more, but there are dungeons to farm for AA. :)