I have that Crucial RealSSD. I didn't want to go under 128GB for the primary OS drive. It fills up so quickly, and I keep all my data on a RAID1 array of regular WD disks. IMHO, running under a 128GB drive for the primary isn't a good idea, you'll run out quickly.
Just between applications, Win 7 x64, and a few games (Crysis, LFD2, and Just Cause 2) I'm already at 61GB.
It's a very fast drive, didn't realize it totally at first, but yeah, it's fast.
As a bonus, I've had good experiences with RMA/returns with Crucial before. That was another factor that went into the decision.