I think it all just comes down to personal preference; on my old bike I had panniers and a racktop carrier (for my laptop) from the start, and only carried a small Camelbak pack on my back. When I bought my new bike, I hesitated about putting a rack on it at first (it looked so sexy sans-rack), and tried loading everything into one of my sleek hiking backpacks. I found it to be much less comfortable, and ended up with a stiff back and such at the end of my ~22km (one-way) commute. I'm back to a rack now and loving it!