DW's 7 year old Dell came with Vista but we immediately upgraded to W7 (free). A new one is in the budget for this year.
As we keep our PCs for a long time in tech years (my 'new' PC is 6 years old), I've been looking at the 6th gen Intel processors. But as you might expect, there is a big price jump between 5th gen and 6th gen. I think I'll go for 5th gen.
She doesn't do anything exotic, but she does a lot of it simultaneously. Not at all uncommon for here to have 10 browser windows open, Quicken, Word x 3, Excel x 6, streaming video and email - all simultaneously. I'm going for a lot of Ram for her this time.