It really depends on the usage situation. For common desktop usage, sure, writes will be covered up by the cache. There was plenty of times though that I could make the cache useless on the linux server hosting the perforce depot at my previous job. With a random smattering of really tiny files, and really large files, the difference between the Intel and OCZ drives above would be noticeable.

Of course SSDs aren't quite there on the cost side to justify replacing multi TB storage systems, especially when looking at the Intel cost. And as you point out, the upgrade above a 10k drive is already noticeable, even with worst case situations showing a minimum of a 2x improvement.

On the desktop, it's getting there. I'm probably going to try and round up an SSD or two here at work for testing, to see if they would work well for the developers. The main concern is still size, though a traditional hard drive could still be used for the stuff that doesn't require the speed. At home, I'm waiting for a 250GB+ SSD to come in below the $2/gb mark. The Vertex series is what currently has my attention.