Yes, that is pretty sage advice from bmhit…if you’re trying to do anything beyond straight editing, then a Mac Pro is going to be the most desirable option.
I attended a day-long workshop offered by Apple last April, for Final Cut Studio 2. We used MacBook Pro 2.4 GHz DP, with 2GB RAM, and 300 GB hard drives, and we did Final Cut Pro, Motion (with some difficulty and very slow response in rendering more than 3–4 layers of effects), Soundtrack Pro (had no problems), and DVD Studio Pro (very slow render “baking” time for DVDs).
As you may already know, Motion is very graphic and memory intensive; the rep their was one of the programmer leads for Motion (as it turns out he’s a former After Effects Guru), and he mentions that if you want to run Motion and Color professionally, you really need the top ATI or Nvidia rated for HD, plus 16GB of RAM (of course the price has come way down on the 2GB sticks), but at the time, it was a $12,000 proposition (Mac Pro, memory, storage, Cinema Display, etc.). Uncompressed HD editing (online) will also require very fast storage via an external dual fibre-channel RAID (i.e. RAID 50 off an Xserve side cart)...
While I have seen MBP running Motion, I can say that if you’re trying to do this for a living, the time lost in slow renders and limitations in # of plugs will probably make the MBP not really a viable solution unless you’re using it as a cuts-only, proofing “travel” rig; otherwise, perhaps wait a month or so for the new releases (Montevinas with faster front-side bus and 4GB max RAM); those may also come with USB 3, which all around are specs worthy of entry-level HD editing (offline).
To get a good idea of what other pros are doing on various setups, check out websites/forums for Final Cut Pro, such as L.A. Final Cut Pro User Group (LAFCPUG.org) or 2-pop.com, etc. Good luck with that.