Yeah, the Constellation series is having some price pressures (1TB for $200? wow), they used to be able to command a significant price premium over similar SATA drives but at 2:1 the extra cost may be worth it for "server grade" drives, and 7200RPM in 2.5" is fast.
However, at $120, the 750GB Momentus XT is a hybrid SSD/7200RPM drive, giving you several GB of flash-speed storage and lower power consumption than the Constellation. I think we've seen one failure out of more than a dozen drives when abusing these poor little things in an awful way, constant dozens of transactions per second for about two years now. I expected to see them start falling over in quantity about a year ago but three of the four spares are still sitting in inventory. The new generation two XT's have more flash and go up to 750GB.
Some friends caught the OCZ 512GB Vertex 4 - VTX4-25SAT3-512G.M - going for only $299.99 just recently (priced normally around $500). Give it about two more years and I wouldn't be shocked to see price parity between SSD's and the Constellations, which basically spells end-of-line for them.