From everything I have seen, a drive with TRIM support will not see any improvement in real life results through RAID-0 on 2 drives. Performance tests have shown "Garbage collection" in real life seems to not work nearly as well as TRIM, but if you have drives that do not support TRIM, then you would see real life improvements by raiding them. I guess there will be improvements on reads, but writes will suffer greatly.
If I am not mistaken, The problem lies in the fact that the OS can not tell the drive when something is deleted or when it is in use. Deleting a file is not erasing it from the drive, it simply removes the pointers to the file. TRIM offers the information to the drive that the file is deleted and thus it can be erased. Without clearing the memory, additional WRITES will suffer.
I have seen some very exaggerate numbers on some of these devices, especially the PCI-E cards that offer such extreme performance numbers. Hopefully the RAID developers can get their act together and start supporting TRIM. Then we may see some really staggering PCI-E and RAID drive performance numbers that will make SSD something amazing.