1) When I started reading some user forums about FCP, most people seem to agree that Apple's claims of FCP's realtime HDV capabilities are unrealistic and overrated. On the PC side, there are many solutions available for editing HDV, such as Cineform in Premiere/Vegas, Canopus HQ in Edius, etc., but on FCP it seems you are stuck with native HDV or transcoding to DVCProHD (which is a more lossy format than the other intermediate codecs). There also seem to be a lot of bugs and gotchas when working with HDV in FCP, such as problems capturing continuous footage with correct timecode, poor quality when downconverting to SD, inability to import M2T files from direct-to-disk recorders, etc.. Many of the "elite" FCP forum regulars on sites such as lafcpug.com actively berate people just for shooting in HDV, which they claim is an inferior format that should be avoided at all costs (even though PC editors seem mostly happy with it). Since I'm already comitted to HDV and can't afford to switch to anything better, this really turned me off of FCP. I hope they are wrong and Apple's claims are right...
2) There are a couple other troubling issues specific to the MBP. Some users report that the screen brightness is not uniform across the screen, this seems to be luck-of-the-draw. There is also the fact that the MBP's Superdrive has a lot of flaws (no region free, poor burning quality on many premium brands of discs, many reports of stuck/jammed discs). Granted, it is an easy problem to get around by using an external DVD drive, but I feel this should not be necessary on a brand new, top-of-the-line product.
3) With the "useful for work" aspects in doubt, its hard to justify spending $2000 on a toy. That money would buy me half of a new camera or a lot of other equipment like mikes, lights, etc.