I recall reading posts within the past couple of years critical of mixers with built in usb interfaces - mainly if I remember, describing the interface quality as not as good as they should be -or not a good match for a stand-alone interfaces. Wonder if this is still considered the case, or is the quality better now in some?

Look up the Presonus Studio Live line. Good stuff. Lots of great reviews.

Not so these days. Presonus make perfectly good mixers with built in converters. I am also mixing an ongoing project with an artist who is recording all her tracks through a Mackie Pro FX 12.  I am not hearing anything bad, only stellar sounding tracks and the mixes sound great so the mixer in this case in definitely not the weak link. She is using a quality microphone and that is really what I am hearing. ie The performance and the microphone are high on the list for a quailty result. The Mic Pre and the built in converters are just not getting in the way.

The Midas Venice mixers also come in USB or firewire versions. They've gotten great reviews.

Only 2 I keep seing bad press about are Behringer and Alesis regurading pour drivers.

I've been really happy with my Edirol M16DX, unfortunately it's already been discontinued.  I'll never find another 16 channel digital mixer / interface with control surface functionality which works this well for such a low price.