I use Vimeo a lot for client previews since videos can be password protected.
The problem is knowing how to export your video so it displays properly on Vimeo. Files like native 1280x720 DVCPRO HD won't always work. I was having trouble with one particular which kept (after uploading and encoding at Vimeo) was VERY choppy and squeezed.
The most reliable way I've found to upload something to Vimeo is to convert it to H.264 first. Specifically I'll either use Export Using Quicktime Conversion… right in FCP or just Export as Quicktime Movie from FCP and then encode that to H.264 using QuickTime (since Compressor is kinda slow).
If you need to do this a lot, go ahead and make a droplet for H.264 conversion via Compressor.
Vimeo really seems to like H.264 as it's upload format. Make sure the aspect ratio is correct and you should be okay. If I get a chance I'll post some more detailed instructions when I (finally) get back home.
Unfortunately you may notice a Gamma Shift with your uploaded videos. That's mostly like caused by the compression tool you used. You'll never get it exactly right but you can get closer using something like x264Encoder from here. Test test and test again, that's becoming my motto it seems.
QuickTime has (and has had) an Gamma Issue for years now. It will force a Gamma of 1.8 on videos and fixing it is a mess and probably good fodder for another long post.
Bottom line for Vimeo, if you have an issue with your uploaded file, try H.264 and re-upload. Keep in mind that if it's not in HD when you upload it, it won't be in HD (or have the toggle option) when you play it on Vimeo.