The Amstrad of the PC audio world
M-Audio do some decent products but sadly they tend to be rather cheap and cheerful. Two years ago I purchased a professional outboard M-Audio USB soundcard with XLR inputs for work purposes. It went straight back. Not only did the drivers refuse to run on the version of Windows I was running (XP with media centre) M-Audio indicated they had no intention of producing a driver despite it being the current version of Windows. The build quality looked like the box might survive a couple of weeks of use before something fell off.
I sent it back and got an Edirol unit instead. Brillient. Worked fine with my Windows laptop and is now working fine with my Mac. Built like a brick outhouse, I've been carrying mine around for 2 years now.
In short, M-Audio, cheap build quality and poor driver support.