J Freak has the right idea...
If you plan on touching HD, it's a MP - hands down. Fibre Channel is a lot easier on the Mac if you have access to dropping in a Apple-branded fibre-channel card, and using their equipment (aka Xserve RAID) [well, I should probably say: It's easier to get support if you need it - Apple likes it that way. ;-)]
That notwithstanding however, I haven't seen a lot of options for doing anything above 2 tracks of SD on a MBP - you would need the AJA I/O or something similar.
A MBP can do more than the 2 tracks of SD that I mentioned, but it takes a fat wallet (so does a MP). I work as an editor, and 90% of the projects that I touch are SD or DV... so it was a MBP all the way. If you are in a similar situation, don't rule out the 24-inch iMac either - that's a killer machine, it's got FW800, big display, and it's pretty quick.
Oh there is ONE MORE THING.. ;-)
Make sure you take note of Final Cut Studio's ENTIRE package when you install it - if you install all the apps and content, it's right around 70GB! For that, the extra drives in a MP would be great...