I will keep playing forever under the following conditions:

The game still works
There are still leaderboards
You can still play with people online

Failing those three things I will play until the game craps out on me (equipment failure or it gets boring playing the existing material).

I will be sure to buy lots of keyboard controllers and MPAs.

Yeah...this game is just too much fun. No plans to quit.

Until I get all the achievements I have left, or until I hit a wall where I give up and decide I've got no chance on some of them, so assuming DLC ends in three months when we think it will I'll probably have 6 months to a year left. I don't usually just play games for achievements, but like someone else said this is really just another way to listen to music and without any real goals left I'd probably give up on it fairly quickly. I might pop it back in every now and then but I wouldn't play as regularly as I do now.

Until I am physically unable to do so.

Never DONE!!!!!
I hope I didn't say that to loudly?! :cool:

It's hard to say in months or years, I'll quit when I'm bored. Having no DLC to buy ever again will hasten that boredom feeling though.

Probably when the controllers break. Which could be whenever. It's hard enough to get guitar controllers now that work well.

I'll keep playing as long as I can do it a full band, online, with reasonable frequency. I know a couple of people who are planning on migrating to the Xbox360. There's no way I'm doing that. I'm not spending hundreds of dollars to jump from one sinking ship to another ship that's sinking a little more slowly.

It does help that the three available artists that I like most in the game (Yes, Billy Joel and The Doors) have only a few GS among them on PRO keys for me.

That gives me plenty to work on.

Oh and zero FC's. Not even on "We Didn't Start the Fire", which I probably should have FC'd by now.

Until I can no longer play so whenever that happens, hopefully not for years haha.