I was going to write an article about the state of Linux audio as far as hardware support is concerned, but not finding the time just now. There has been some involved discussion about the state of interface support and documenting hardware support on Linux Musicians. There's lots of uncertainty about what hardware works and to what extent. I researched this a while back and found it confusing. I went for my M-Audio Delta 66 as it is very well supported and does what I need, despite being about ten years old. I've been considering my next PC build and will either have to make sure it has good support for old PCI cards (seems some chipsets do not) or look for an alternative interface. I have looked into some of the developer mailing lists to see if hardware support is improving, but they are mostly too technical for me. The main area of interest seems to be USB 2.0 as that should handle the needs of most small studios. Apparently some interfaces do conform to some standards in order to be usable with iPad, but it's not clear how well they work with Linux.
Luigi Verona has written a nice blog post on the state of software. This has stimulated a big thread on the Linux Audio Users mailing list. I don't subscribe to that, but I try to check on the archive to see what is happening.
The latest version of the FFADO Firewire driver added support for lots of devices, but it seems that Firewire is losing out these days. Their usage statistics are interesting to get some idea of the size of the userbase. There seem to be a few thousand active users. It seems like that could be viable for commercial support if some manufacturer would work with them to improve the support, but is probably still small compared to other platforms.
I still haven't managed to get KXStudio installed. When I got around to trying in the last week I found I didn't have a flash drive big enough for Ubuntu Studio. I've not ordered one and hope to try again soon, probably just before 12.10 is released. I need to get something up and running for the next Six String Bliss album project. I have a track in mind that will stretch me musically and technically.