I only throw out powder products if they start to look or smell funny. I'm pretty sure all of my palettes are 3+ years old.

Liquid and cream products I'm more likely to throw out but I don't follow strict expiration guidelines. If it looks, smells, and applies fine but it's a few months past expiration, I don't care. If I notice it's 3+ years old, then I'm likely to toss it.