I've used one. There's noise at about -70dB on all inputs via firewire on mine. Not the end of the world for live recording, but I was disappointed to find it. Others (see
www.cakewalk.com forums, 'gear' I think) have also reported this. Possibly for other reasons, but the only times I've had Sonar crash have been when the Phonic control panel is loaded, on 2 different computers.
There's a 3rd party driver -
www.centrance.com I think - which promises lower latency etc. for about $50-70.
But it's the cheapest way i could find to get 16 channels of balanced mic/line input, and you get an analog mixer thrown in.