1) You could use a new font (hopefully just a CSS change).
2) The invision skin looks good... but your buttons could use a little work.
3) Just my opinion, but the banner looks a little childish.
4) In the non-invision skins, you don't define your borders very well and it ends up looking kinda blended, instead of seperated.
5) Your banner should be the width of the page... having it slightly less wider than the rest of the site gives it a funky look.
6) Sometimes your "fine print" is too fine. Don't use bold for fine print and pick something that can be read (ie. Tahoma font?).
7) I have to echo Thantos on the suggestions he made. Don't use tables, and link your CSS files. If you don't link your CSS files, you remove 90% of the power that it wields.