I have a brand new Time Capsule 2TB and a 2007 Macbook Pro (SantaRosa) connected on WiFi. I attempted to start a new backup, but it has only transferred 2GB in two days, and says it'll take approximately "99 days." This problem occurred since upgrading to Mountain Lion. Of note I have two other computers (2011 Macbook Pro, 2011 Mac Mini) also connected via wifi and they completed their fresh backup in a couple of hours.
P.S. The reason I bought a brand new Time Capsule is because I previously had an external hard drive connected to an Aiport Extreme and had repeated failures when upgrading to Mountain Lion. I started this thread:
Therefore, I've concluded that OSX Mountain Lion has a problem involving SantaRosa chipset Mcbook Pros, WiFi, and Time Machine. And I've now wasted money on upgrading my equipment (Airport Extreme to Time Capsule) and still have the same problem - I can't backup my Macbook Pro.
MacBook Pro (15-inch 2.4/2.2 GHz), OS X Mountain Lion (10.8.1)