I have a really shaky shot in a film I'm editing right now (FCP 6.0.6) that cannot be cut from the movie or re-shot. What's the best way (plug-in?) to "fix" this?

I tried a facotry plug-in called "smooth cam" in FCP and it looks terrible.

There are limits to what any software-based tool can do and you need to read carefully about how the filter works and try different parameter settings, but try Core Melt's "Lock and Load" which is by far much faster and more accurate than Apple's Smooth Cam filter.

I would like to add my endorsement for CoreMelt's 'Lock & Load'. It can be magical in rescuing unusable footage & making shots that are OK but a little jittery look perfect. There is a 15-day full functional trial version available so you have nothing to lose by trying it & seeing what it can do for your case.

I will check it out. Thanks guys

Fix the problem in MOTION! Use the stabilize in motion. Its quick, accurate and you already have the program. The round tripping is simple so you have nothing to lose!

If you don't know how to use motion I recommend you learn. Once I learns how to do the stabilization in Motion so many more clips became usable than before.