Some pictures and a nice pax interview in this news story, sounds like the United crew and staff handled things well:
Plane slides off taxiway at Spokane Airport
From the marks in the snow, looks like the aircraft slid sideways into the snow bank, hopefully no damage.
And speaking of B-737's going sideways on the ground, here's some PPRuNe discussion of why they sometimes seem to taxi with a crab:
http://www.pprune.org/tech-log/18831...ng-ground.html