I think if you're trying to build a rig worthy of the velociraptor, the noise level will be moot, since the fans will likely be louder (assuming you use air to cool the computer). I've got 2 150GB raptors in raid 0, and even though they make some noise on start up, they're not too bad during use. The fans in my case make much more noise.
Supposedly the new velociraptor is just as fast as my 2 raided raptors too. I think its performance is likely fairly close to most SSD drives. Vista + OSX are only now starting to redesign their packets to work better with SSD, according to this.
I've heard that some SSD, including OCZ can have unexplained data loss.
At this point in time, I would only go SSD in a tower if you are hellbent on speed. Not as a reliability option.