modulator: I agree, the FF400/800 are some way ahead of the competition in their price range. From what I've read about the iMac incompatibility issues:
1. The FW800 to FW400 cable seems to have worked for some people, but not others
2. It's possible that, for whatever reason, the 24" iMac has caused more problems than the 20" model (though this may simply be because Apple have sold more 24" than 20", so more people are discovering and reporting problems with them)
3. The same issue seems to be affecting other FireWire audio manufacturers--notably stuff from Mackie/Tapco--and has been since OS X.4.9 onwards. Presonus and Digidesign aren't even claiming to be compatible with Leopard yet. MOTU and M-Audio are supposedly OK, although in the case of the former, having checked out unicornation.com it seems that the 828MKII has a few of its own problems going on under Leopard
4. Connecting your FireFace via an external HD seems to be the only effective method at getting it to work at the moment. However...
5. ...Either the same FireWire issue, or a separate one, is also affecting some non-audio devices, including FW hard drives (I've seen Western Digital mentioned on the Apple forums)--so if you're planning on daisy-chaining your FF, and you don't already have an external HD, it's worth researching carefully which one you're going to get.
At the moment, no one is claiming responsibility for the basic problem--I haven't seen any official statement from Apple or Agere. RME's line--as, I might say, appears to often be the case--is that they won't accept that there is a problem with their own hardware/drivers unless/until they have specifically located and diagnosed it on one of their own machines. Which is fair enough; how can they understand a problem if they haven't encountered it on their own test rigs? However, at the moment we are lead to believe there is a fundamental incompatibility between Agere's chip's and RME's; considering that, with some messing about, I've got my FF400 working fine on this supposedly incompatible Mac, and some other users have done the same, I rather doubt this. Considering other manufacturers are having to release new driver/firmware packages to get their products to work with Leopard, I find it hard to believe that RME can get away without doing so--and it seems they can't.
I note with interest that elsewhere, it has been mentioned that "New firmware had to be released earlier this year by manufacturers of several USB interfaces to work with system updates for both OS X and Vista, despite some of them blaming Apple etc. at first." We all have to remember that Leopard is a new OS running in many cases on new computers that use different components to that which a lot hardware released even last year was developed on. Given that, it's not entirely surprising that there are problems arising; when DOESN'T something like this happen with a new OS?
That said, I maintain that it would be nice if one of the companies involved were to provide us with either a timescale for when these problems are likely to be resolved, or at least some news on what progress (if any) has been made so far. It angers me to think that we, the consumers, are sat around feeling frustrated, and unable to create, whilst it's entirely possible that the people who should be fixing this for a living are letting the days go by without really pushing for a fix (this is not a dig at RME, or even necessarily the others; just an inevitability of being in, as someone else put it here, X% of RME users using X% of incompatible Apples).
PHEW... right, I've spent far too much time on all this. I'm going to get back to MAKING SOME MUSIC :-D