I don't know if this will solve your problem, but this is what I do.
After I have resized my jpeg file til websize (72 dpi and usually 600x600 or 660x660 pixels) - then I run a very "light" unsharpen (USM) filter ON the resized web page, before I save it - I don't have PS here on this PC, but my parameters on the USM is from top to bottom : 15-1-1. I have experimented some with these numbers and these are what I am usually happy with. Gives just a little sharpness to the uploaded page.
Hope that helps.
