Do the keys "feel" right? Are they sticking, harder to press, springier, etc. than in the past?
Here's a highly technical maneuver I learned from an old NASA mechanic:
1) Turn it upside down
2) Shake it like an Etch-a-Sketch(tm)
3) Try not to hurl at all the crumbs (Cheetos, natch), dust, hair, and random skin flakes that shower your desk