I was going to chime in and say, "ahh, but GPUs are worthless for everyday tasks!" when I realized that my 4-yr old MacBook is just fine for every day tasks. For scientific computing GPUs seem to be a great way forward. The pain and complexity of writing parallel code is mitigated by the fact that, hey, scientists are writing it.

For normal, everyday usage I see no reason why 3.5ghz is any better or worse than 20ghz. Or 2ghz, for that matter. The 'computer' my mom is most excited about now is her iPad 2, which has less power than the workstation I built in high school.