Riding 23's the other day in the slush felt pretty sloppy / unstable to me. I also had to be really careful and slow with taking corners.

Riding a mountain bike with knobbies last year in Portland when it dumped felt pretty damn stable and natural.

If I lived in an area that had snow on the ground for a constant three months or so, I'd say a fixed mountain bike w/ knobbies or studs would be the ultimate work horse / utility bike. Lots of fun for sure.