I have a Kingston SSDNow 90GB drive. SATA III, 6gb. My motherboard is SATA II, 3 gb, so I got an adapter card (Koutech) for 6GB. The SSD was $90 with a $30 rebate. I pulled the trigger on the ole CC. (Credit card).

I tested it against an old but fast Seagate 250 GB.

System is AM3 785, Phenom II 4 core clocked to 3400. 8GB of RAM.

Here is a nice way to test your drives (Windows 7, maybe Vista or XP):

Go to start and type in CMD. RIGHT click on CMD and left click Run As Administrator. Type winsat disk, then hit enter. The test will begin.

The results: (SG means Seagate)

Sequential 64 read SSD 299 MB/s, SG 86 MB/s. SSD 3.5 times faster!
Random 16 Read SSD 159 MB/s, SG 1.67 MB/s SSD 95 times faster!!
I repeated the tests and got the same results!!

RESPONSIVENESS:

Ave IO (input/output) SSD 0,68 ms, SG 4,25 SG 6.3 times slower!!
grouped IOs 7.8 units SSD, 13.14 units SG SG 68% slower
Long IOs SSD 1.49 SG 16.3 SG 11 times slower!!
overall SSD 11.59 SG 214 SG 18 times slower (double checked!!)

Sequential 64 Write SSD 226, SG 92 SSD 2.5 times faster
Latency 95th Percentile SSD 0.83 SG 45 ms SG 54 times slower!!
Latency MAX SSD 50, SG 283ms (micro seconds) SG 5.7 times slower!
Ave read times for random writes SSD 0.28 ms, SG 11.1 SG 40 times slower!

If you got a motherboard that has "Smart caching", you can run an SSD along with a normal HDD, and it will cache the OS, and most used programs on your SSD. So basically you get SSD speed on a whole lot of things, without sacrificing storage capacity. That is how I got my rig setup. Only Intel motherboards support this. And you need a Z68, or Z77 motherboard. If you can afford a 250gb + SSD you would still be way better off going with that, and using a USB storage drive to store the junk you can't fit. But with the smart caching I got a 64gb SSD + a 2TB HDD.