RAID0 boot times aren't any faster because it's a software RAID. The system has to load the kernel cache off the boot drive (a copy of the cache files should be on both of the drives,) which it is only going to do from a single drive. Once that's done, and the software RAID kext(s) have loaded, only then will you get the performance boost from the RAID0 configuration. But, by that time, most of the boot process is already done.
If you want faster boot times with RAID0, you need a hardware-based RAID configuration ... which doesn't exist in laptops, to my knowledge. Then again, when you have a hardware-based RAID controller in the system, it increases the POST time of the system too, so in the long run, your boot times (starting from power-on to login) probably won't be any faster then either.