It's ok - common subjects should get repeated, and people can refer to old posts as needed. In fact, on BeginnerTriathlete, which is an excellent and very useful forum, moderaters make it a point to allow repeated asking of beginner questions and not just making hard stickies for them because you never know where the conversation will go. One great beginner thread about basic swimming morphed into a big debate including 2 professional swimmers, a 3-time US Gold medalist, and several elite triathletes. (Yup, hanging out on the BeginnerTriathlete forums).

Backpacks are great for short commutes, especially if you have no permanent place to put your panniers after the ride. Students have this problem, especially.

Lugging panniers around all day SUCKS beyond belief. They make walking a royal pain. It's far, far worse then the trivial incovenience of riding with a backpack. If I know I'd be walking around all day as a student with my panniers, it wouldn't matter how long the bike commute is - I'd definitely go backpack.