The SouthPark TV series was done using 3D software from day 1. (The Santa vs. Jesus short that got them the gig was done with pieces of paper.)
When you think about keeping track of a bazillion pieces of paper, it makes a lot of sense. They also aim for a lead time of "idea to finished show" of something like 6 weeks (so they can be topical) -- which is unheard of for an animated show. Network live action TV shows go from pre-production through to post-production in 3-6 weeks (with three shows, one in each stage, at a time); by contrast, an episode of The Simpsons takes over six months.