I recently updated and jailbroke 3.0 on my 2G iPhone
I got everything i liked re installed (themes) etc.
after about a week the icons seem to "deteriorate" one by one, starting from the top of the icon. it doesn thappen to all the icons, and if i activate a different theme, they go away, and look normal. after about a few hours, the "deterioration starts.
ill attach a picture so you know what i am talking about.
lol? crazy. I would suppose that some kind of theming/skinning application is responsible for this. try to uninstall winterboard and see if it still happens.