Okay, since everyone is just stating on what to get, I'll instead give FIRSTHAND experiences with Final Cut Studio 2 on a Macbook.
Like some people have stated, everything that doesn't use the GPU for processing (such as Color & Motion) will work just fine. There are some filters on Final Cut Pro that won't work, because they require a powerful GPU to process the effects. Anyway, for the most part, it works flawlessly. I've never had FCP crash once on my Macbook, and I've used it for the past two years, from Final Cut Studio 1 to 2. Just make sure you have a decently fast external to work off of.
As for speed comparisons between a Macbook and a Macbook Pro, they're negligible. I used to have a Macbook Pro for work, and a Macbook for personal use, and I've gotta say, that the Macbook felt faster for some reason. Keep in mind that these machines were 1st generation Macbooks. So there was a 2.0 Ghz Core Duo Macbook vs a 2.16 Ghz Core Duo Macbook Pro. Both had 7200 RPM internal drives, and speed was nearly identical, with the Macbook Pro edging out the Macbook by a few seconds, but nothing big enough to warrant the extra cost.
I've also used Motion on my Macbook for a few occasions, and again, I've actually never run into any major problems, just as long as you aren't going super insane on effects and such. Otherwise it'll lag big time.
If you NEED to use Motion + Color, then yes, the extra cost would be worth it. If you have After Effects CS3, then you won't need to use Motion and you could use it on a Macbook just fine. IMO After Effects is a more versatile motion graphics tool than Motion, for now.
So it brings up this question: am I ONLY going to be doing video editing? Notice how I put emphasis on only. If the answer is yes, then a Macbook will suit your needs perfectly. Obviously, if you want to be future-proof and be fully supported on pro software, then get a pro machine.
I've gotta ask you one question though. Are you going to be working with HD or SD? If you're working with HD, then it's a no brainer to get a pro machine, since you need all the processing power you can get.