I used to commute to school (30 mi rt) with just one ortlieb pannier, which held books and a change of clothes. This term I've found it necessary to obtain a laptop, and while it came with its own backpack, this backpack sucks. I tried it today and found it the most painful commute in history. So, I won't be doing that again. I've also got a timbuk2 messenger bag which I use from time to time, when I don't have much to carry, but it isn't padded like the backpack is. Finally, I also have a gregory backpack with a hipbelt which I hike with, and which carries great but I haven't tried it on the bike before.
So here's the question. I vastly prefer carrying everything in the pannier, and I'll take two if I need to, but I wonder how good it is for the laptop to ride there. Obviously I don't plan on falling, but even outside of that I worry about vibration. On your back I would assume there's some buffering in the vibes, since they travel through half your body before getting there. Are they that significant, and if they are, is there a way to mitigate them if I wanted to put the laptop in the pannier? Are there other variables I haven't considered?