Coding of the driver has commenced but there is no ETA at present.
Update, 6 January 2011: development of the driver with the ff400 continues and is approaching usability now. Refer to the update on the FF400 device page for full details. Once the ff400 has proven to be operational I hope to bring the ff800 up soon after. Despite the two interfaces differing in important ways I don't see any major complications associated with the ff800 at this stage. There's no estimate as to when this will be done, but I'm currently hoping for around Q2 this year. I'll try to be a little more timely with updates too.
I thank ff800 owners for their patience - I hope to have something for you soon.
Update, 17 April 2011: as per the main announcement, a preliminary driver is now ready for testing with FF400 devices. FF800 devices almost certainly will not work yet. However, once this proves to be operational on more than just my test machine and the mixer has been made useful I will be refining the FF800 sections of the driver. I am hoping the FF800 will follow on from the FF400 fairly quickly due to the reasonable level of commonality between them.
Update, 27 April 2012: the driver is approaching a state where it should be usable for most people now. There are a few known outstanding issues and these are being worked on (most notably, an occasional failure to cleanly start audio streaming). TCO support is planned. "Support status" has been changed to reflect this. Test reports and suggestions are welcome. Note that support for the MIDI ports is not currently implemented.
Update, 23 December 2017: TCO support has been added in FFADO 2.4.0.