I've got about a terrabyte of data (mostly films, home movies, music and photographs, all badly in need of rationalising, but it's easier to throw disc space at it than rationalise it) which was distributed over 3 x 500 gig drives.
Now I've got the same amount of data on one huge raid drive (made from 3 fresh discs).
I'm keeping the original discs as backups (offsite).
I know I'm taking a risk, but it wasn't actually that much grief transferring the data from the 500-gig drives to the new raid drive. I just let them copy overnight.
Backing up new stuff will be more of an issue but I have here a box which I intend to stuff with 3 big drives and back everything up remotely with Rsync, or similar. Until then I'll just put important new data on an external USB drive.
I don't think there are any major issues with OSX's raid implementation. I've used various IDE (PATA and SATA) raid controllers, but never again. The only way I'd consider hardware raid would be top-end stuff.