OldVersion.com has been around for a long time, I think if they were modifying binaries or embedding malware, something would have come out by now. The economics of a site like this also encourage making yourself a legitimate source.

That isn't to say it's 100% safe, and this type of thing has certainly happened in the past, but until something comes out I think they're relatively trustworthy. I wish all software vendors made old versions officially available, but they frequently don't.