I too have the SD600 in the UK recording at 1080/50p. No, iMovie '08, 09, and (whilst I haven't got it the general opinion seems to include '11) do not natively support 1080 at 50p or 60p.
I've always used iMovie 06 or Final Cut Express (which to be fair don't handle that resolution either) so I'm not fully up to speed with what I refer to as the 'iTube Trilogy' - In short, the latest '08, '09 & '11 products should be shipped under a different name than iMovie - They are more for assembling clips and posting them online or by email. IM '06, FCE and Final Cut Pro are movie making software packages.
So, your options .................
Record in lower / 'standard' AVCHD resolutions. These 1080i formats are fully accepted by iMovie '09 /'11, but be warned.... Whilst I have little experience of the iTube Trilogy, the general verdict is that to handle interlaced footage, they remove every other line of resolution, so downgrading your beautiful camcorder footage before you've even started. Fine for Youtube, but not good for DVD's or movies.
Record in 1080p and save your video to an external hard drive for a future day when video editing software catches up.
Record in 1080p and save your video as above - Then use a couple of applications / utilities to get your footage into iMovie. Look through other threads and there are quite a few tips and tricks about getting the best quality from iMovie. In quick summary ......
Movist - A free application that can view mts files. You will need a fast Mac to play them at that sort of speed and resolution progressively
Convert your mts files with a couple of utilities that will allow your movies to be imported into iMovie. ClipWrap, VoltaicHD are inexpensive utilities that will take your mts files and rewrap them in a file format that iMovie understands. There is also a free Automater Utility called rewrap2m4v which I have used very successfully and I think it does much the same thing. Preserves the resolution and frame rate and effectively just renames it as m4v so that iMovie can import it.
I like iMovie 06 at 720p resolution, but this has a limited Frame Rate of 25fps, so effectively removing every other frame of your 50p footage. iMovie '09 / '11 will maintain resolution if keep your footage progressive throughout. This software also likes to work in 25fps but there is a software work-around to increase the frame rate to the original 50fps utilitising a utility called Plisteditpro.
So, as a final answer to your question, iMovie '11 won't accept your footage out of the box. But you can use a utility such as ClipWrap to repackage it as an acceptible movie format at full resolution and frame rate. You can use plistedit to change iM '09 (and presumably '11) to accept 50fps and then you should be able to edit (on a fast mac) your movies. My personal solution is to record at full 50p and save for the future, then rewrap the files and edit them in iMovie '06 at 720p25 where I am downgrading both resolution and frame rate, but they still look beautiful enough for my humble needs.
Good luck and great choice of camcorder.
