It should always be the last step becuase it's so destructive, but depending on the application, i'll sharpen in the RAW converter slightly which is generally enough, but if I print huge, i'll do it after resizing too.
and when you interpolate in 10% steps up to your size and then sharpen, big enlargements can look great. i've got some 20x30's that came out awesome that way, often being as sharp or sharper than the medium format film that gets scanned in by my classmates.
I'm not sure how he did it, but Thom Hogan in his D3x Review has a 100% crop from a D3 that's been uprez'd that has just as much detail as the D3x SOOC.
I've been meaning to email him about that..