After reading and hearing everyone raving about SSDs for a couple of years it was hard to resists the upgrade.
So I got an Intel SSD 510 120GB to replace my Seagate 2.5" laptop HDD.
The prices in the ~120GB SSD category are pretty close. I chose the Intel based on reading that they have a low failure rate (I was unable to find the soruce when writing this up).
The Thinkpad X61 only has SATA-II; the drive supposedly has better performance on SATA3.
UPDATE: Samat K Jain points out that "the ThinkPad X61 is limited to 1.5 Gbps, even with SATA-II (Lenovo's excuse: power saving, by keeping bus clocks down)". Lots of discussion about that on the net.