(Little late clarifying my own opinion, but...)
In addition to the ease of installs/updates/troubleshooting (no way to just pull out the boot drive to test something), there's also that it's sort of a waste of speed.
Generally a RAID0 setup isn't going to make all that much difference on the sort of disk performance that affects OS loading and operations, and application loads. Where RAID0 excels is raw throughput, for things like video capture.
Further, if you put your boot disk on the same disk/disk set you're using for your data needs, you're going to be increasing the likelihood of fragmentation and needlessly slowing down whatever operations you want maximum speed for, since the drives will have to seek to do OS operations in the middle of whatever large transfer is going on.
Thus, it generally makes way more sense to have your data volume be the one with RAID0 and just have a nice speedy single drive (Raptor, for example) for the OS partition, or RAID1 set if you really want the uptime.
If you want some numbers, have a look at StorageReview's opinions on RAID--their tests are admittedly for Windows, but I expect their conclusion (RAID0 on a boot drive doesn't really get you that much extra speed) would be the same with the MacOS. Linear, large-file transfers (i.e. video capture), is a completely different matter--BareFeats has plenty of benchmarks on that.