Thank you all for the excellent feedback!

Questions:
Anyone worried about theft? of the stuff inside the panniers, or the panniers themselves?
Are they any commuters who don't use panniers? why?
For those using the multi-function pannier/backpack - how do they function at their separate tasks? Anyone worried about the straps getting into the wheel?
Anyone dead set on just using a backpack? Why? Do you think they are ergonomic for bike use?

Thanks again, you guys (and gals) are awesome!