I have my primary (1.5tb) drive connected to a 128gb ssd via a Silverstone "hddboost" unit. What this does is clone the first 128gb of your hard drive to the SSD. What you do then is to keep your hard drive defragmented with the OS and program files organised towards the beginning(cached) segment of the drive. When you do this make sure you put your page file to another drive so it and it's continual changes do not get cached to the drive. The bonus of this is that it is seamless, If I have the SSD die I can just replace it and off it goes and keeps working, if i decide I don't want it anymore then I just bypass it and the Windows install keeps working without missing a beat (I've confirmed that this is the case out of curiosity)
Once you've got all your programs installed and have everything running it seems to keep ticking along quite nicely and provides a performance boost around midway between using a SSD and a platter drive by itself. Now this doesn't help you if you are one of those sorts that just cannot keep well enough alone and continually tinker with your system as changes will have to be re-cached and the boost will be negligible until it has gone and re-cached that first segment of the drive.
I've also got a slightly different system set up for my Steam games drive. Namely a Highpoint 1220 caching controller along with another 128gb SSD. I initially bought this second system to use for my boot drive but as it turned out to be such a massive pain in the ass to set up I ended up giving up and buying the Silverstone device and relegating this to caching my games drive to see how it would go performance wise. After some initial positive results many months ago I kept it on my system as it did improve things noticeably.
Oh and for those that care for such things, other specs for that system include 12gig of ram and an i5 3570, so I wasn't just upgrading one subsystem to the detriment of others.