I typically try to stick with one game at a time nowadays, especially since getting a SSD. If I get stuck then I stop playing but always keep my savegames to come back to, some games I came back to several years later (Halflife, GTA3), for example my System Shock 2 saves are over 7 years old but I haven't deleted them.
One thing I do have a tendancy to do however is play rubbish games almost in the hope that I can say "that's rubbish, I'm moving on", for example I'll just fire up a 3 year old mediocre FPS/racing game that was rubbish at the time never mind now, something I got in a big pack on Steam or whatever. Something that is quite shallow and easy to get into - occasionally I get pleasantly surprised but it seems a bit silly to do this when I also have plenty of 90%+ rated games sitting around unplayed.
The problem I have is finding the time to grind out some games, I've recently started gambling a lot more and that is almost replacing my gaming, I can easily spend 20+ hours a week working out bets etc. In theory I'm playing The Witcher at the moment but I haven't touched it for a couple of weeks.
Funny thing is in some ways gaming is a bit like a chore, in that I like completing games so I can move on to the next one, whereas in years gone by it was really disappointing for a great game to come to an end.