One thing that has always bothered me as a proaudio user, is the lack of support for a wide-range of audio interfaces.

Generally usb1.1 devices are fine, but USB2.0 was ugly with no standization for these types of devices (which USB1.1 did have). Companies tended to use very different methods with USB2.0 (and firewire devices). So it has taken a long time to get a wider assortment of proaudio devices working with Linux on an acceptable level. This situation has and is improving, but it can still be a difficult proposition finding a decently supported card, at your local music store. Often, it is easier to shop online, and grab exactly the card you are looking for (or ordering through a store).