About the hover effect: No pictures, I'd say. Good hover effects can be done with css (colors, background, light, fading, even moving is no problem).
About the pictures sizes: can you make the background pictures smaller and cut out the non visible part of the header logo? 235 KB just for some background is way to much. I'll do the whole navigation bar (border, background, font) in pure css - ok, the navigation background maybe tiled, but with a 10x10 pixel png at max.
There's still a lot of people that don't have hugh bandwidth internet access or old browsers that render slowly.
Some sight view: http://openclonk.org/
for example, uses around ~50KB for the whole site design (including background, tiles, css; excluding content like screenshots of course) and it looks great.
I think we should target around 50KB, too (less is better, 75KB at max).
I don't have any instant messaging tools/accounts and I don't plan to use them