The YouTube Multi-Video Uploader is causing some people's computers to become caught in a loop between the upload and install pages. We are aware of this issue and will update this post when it's resolved. In the meantime, if you're experiencing this problem, you may want to try using the single video uploader.
Update (2/28/2008, 4:35 PM PDT):
We've been able to fix this issue. Uploading through both the single video uploader and the multi-video uploader now work properly.