My laptop has a Core 2 Duo T7500 2.2GHz. It's fine for basic recording at least up to 16 simultaneous tracks--I did some brief experimenting with more and it seemed okay but I've never had a real session go more than that.
I frequently play back 25-30 tracks at a time--again no problem.
When I start adding real time effects, things can get choppy pretty fast if I don't use tricks like buses and freezing/locking tracks. Exactly when problems start depends on the combination of effects...some are far more CPU intensive than others.
All the above is with Adobe Audition. I'm also pretty picky about keeping other nonsense on my computer stripped down to the bare bones to keep my DAW work reliable.
So, basically, what the above tells you is that "it depends". It depends on what DAW you use, how your computer is set up...and what you want to do with it.