I've had mixed results.
It seems to work great if you have some kind of Raid going, the more the better.
I have a machine with 4 SSD and a caching raid controller and it smokes all of the time.

I also have tried using the same brand of SSD (Intel) on a laptop and a EEE-box and find they have moments where they lock up for a second or two under heavy loads. So for me it seems like if you only have one drive it's not that great and when you have several it smokes.