Add a 3rd vote to using it as a Cache drive. The HDD in my main rig is mainly just used for my Steam folder, and I have a 128GB(64GB usable) OCZ SSD that I use for caching with the HDD. My frequently used Steam games load so much faster than when I just had the HDD by itself.
You do have to set the SATA ports to RAID mode in the BIOS though, but that doesn't really cause any issues and TRIM still works.
Also, as a minor side note, when I was setting up the SSD as a cache for the HDD, the option to use the SSD as a cache for the HDD wasn't available in the RST control panel at first. I discovered that I had to go into Disk Management and shrink the partition on the HDD by 50MB. For whatever reason, RST requires a small amount of unallocated space on the drive you are setting up for caching. It took me forever to find info on that.
Oh, and be extremely careful if you use Maximized Mode. I found out the hard way that even a simple BSOD from an unstable overclock is enough to completely trash the entire drive and make it unreadable. Now I stick to Enhanced Mode so reads are cached and fast, but writes are still as slow as writing to the HDD by itself. But since the HDD is just a storage drive that I'm rarely writing to, it doesn't really matter.
