I've seen film of his games against LSU and USC, and while it's hard to compare two players when they are different leagues, I can see why some would compare him to Favre. The USC game was horrible, he was forcing it into some tight spots and as a result ended up with 5 INTs.
That said, I was also extremely impressed with his arm strength. When Taylor would throw the out routes to the flats last year, there was a tendency for them to float. I was always worried that some corner would have an easy pick-6 from it. Keller, on the other hand, has a LOT of velocity on the ball. The LSU game was on ESPN Classic, and this was right after he transferred to UNL. It was exciting to watch, he definitley has a cannon. The physical attributes are there for him to be a 2nd round pick, it all depends on how well he plays.