I had the suspicion before, but now I’m almost certain the corrupt rars are due to mediafire somehow. It’s only ever mediafire uploads, and I check the rars in WinRAR and 7-Zip before I upload. The ones upped to megaupload always seem to be fine, except for the fact that megaupload files get taken down more often. Ugh.
I used to upload almost everything on the weekend in a batch and post them over the week, but I think whether they’re corrupted depends on the time you store them on mediafire. If you upload a batch of files, the entire batch will be corrupt or none will. So I’ve taken to breaking them up when I can. But it’s a hassle.
When people wonder why rapidshare is used so often, this is why. They’re actually the most stable, despite the annoying queue system to get your file.