From personal experience, here is my take.
For SSDs that use MLC storage, RAID-0 would help greatly. Putting them in RAID-0 resolves some of the write issues they have, especially with multiple files writing to the drive at one time.
For SSDs that use SLC storage, RAID-0 is not needed at all. I have 3 Samsung 64GB in my desktop and I was curious to that same question about RAID-0. I ran a benchmark with one drive and compared it to the benchmark with two of them in RAID-0. Much to my surprise, the SLC drives in RAID-0 did not improve at all. The performance was right on par with a single drive, even after multiple tests.
Putting a SLC SSD next to a Velociraptor, the SSD wins...hands down.