I ran a RAID 0 as boot drive in my PowerMac G5 for many years, I always kept two hold option bootable clones on standby.
Booting off the machine was faster, but the OS and even programs still had to initialize, they didn't appear instantly.
Loading of programs didn't make too much of a difference as they were small, a lot of benefit seemed to occur when I cloned the drive to another RAID 0 as the second drive had to be just as fast as the first to realize any benefit of the speed in transferring files, else it defaults to the slowest drive speed.
Running of programs for the most part didn't make too much difference, unless I had huge files to open or duplicate, then the fast boot drive kicked in. But it was like driving a race car in downtown New York, racing to the next light just to stop, then race to the next light and stop again. Without a always huge road of data for it to run fast with, it was pretty much worthless.
If I multi-tasked with my huge 30" monitor, having a couple of TV's on, web, email , music playing and other programs, the faster RAID 0 boot drive came in handy. However I learned over time, that I was comfortable with running only one or two programs at the same time. Having ten programs, 6 TV channels on, ripping DVD's on the side and all that was too much to handle all the time.
The older machines like mine were limited by RAM of 4GB, so that's why a fast boot drive made such a difference as there was a lot of caching of memory to the drive.
These new 2011 MacBook Pro's have really fast i7's and the ability (Apple says only 8GB) to have a max of 16GB of RAM (price is still up there about $900 and coming down)
Lots of RAM, no need to swap.
I guess I got sick of the hard disk speed issues when using iMovie and the like, having 400GB of video on my mbp ment tasks like re-index took for ever, even opening iMovie was tedious. Lightroom was the same, and a simple task like backing up the catologue upon exiting was dreaded.
I hardly ever find the CPU a bootleneckm it was allways the disk, and for what I do, 8GB would not help as much as RAID 0. IMO CPU's particually the i7 Quad core with HT is leaps ahead of the rest of the hardware, and for apps based around video and imaging, it's not likly to be your problem, unless your into 3D rendering
If you want to video edit on a MBP, you need lots of space, and the faster the better.