I got a Fenvi caddy from a seller called Segoo. I just did a test run and it works. I actually have triple boot on the macbook:
OS X 10.6.8 on Intel 320 120gb SSD via Optibay Caddy
OS X 10.6.8 & Windows 7 on default bay 1TB 2.5" 9.5mm drive.
I only use windows for web development and some games. I've decided to allocate 150gb for Windows 7, 20gb FAT32 for sharing (since I'm in school for web development, I'll need a partition to be able to read and write from both windows and OS X without MacDrive, I don't want to use the software). The remaining space on the 1TB drive is use for storage, music, movies, photos, porn and backups accessible predominantly from OS X 106.8 on the Intel 320 SSD drive in the optibay. The SSD drive is used *only* for boot and basically holds NO document files. It is however used as a downloads drive for Firefox but not for Transmission (I download single files up to 10gb large, that kind of frequent write/read/delete/move on the SSD drive would degrade its performance).
It really depends what kind of file system you've got setup. But this should give you an idea.