First of all let me say that I’m using Final Cut Express, but I have no reason to believe that my experiences would be any different with FCP.
I just recently purchased the Sanyo Xacti VPC-FH1A and have been using Iframes with Final Cut with no problem. It appears that Iframe is nothing more than a different flavor of the MPEG4 format. As such it is VERY Final Cut friendly. Unlike my experiences with other cameras which may use AVI or MPEG2 formats, I have not found it necessary to do any conversion before using the files.
Now it is quite likely that many of the bells and whistles of the Iframe format have not been implemented. But even as is, the Iframe format posses no problems.
If Apple has not bothered to update the Iframe capabilities on Final Cut Express or Final Cut Pro, it is probably because it already works so well that they do not feel any pressing need to get around to it.
Well that is my two-bits worth.
Peace
David Courtney