http://skipscreen.com/
https://addons.mozilla.org/en-US/firefox/addon/11243
It does just that; skips the wait screen for most file sharing sites and lets you download the file instantly. iono bout you guys, but I think this is the most awesome add-on you could want here. Works for Firefox.
P.S. Should this be stickyed as a useful topic?
—Desert_Eagle
For MegaUpload it literally skips the wait time which is amazing. For RapidShare it still has to go through the timer but at least it download DLs as soon as it can so you don’t forget about it until the link expires and you’ve gotta wait again :D. Highly recommended addon.