I have a large old Eddie Bauer daypack, and I don't like it for biking. The shoulder straps pull on my shoulders as I reach for the 'bars, and it ends up feeling like a breathing constriction. I've test-ridden with my laptop briefcase in the small of my back with a load of PC and such, and that works if it stays in one place. Hence the messenger bag idea. I'm leaning toward a Chrome with an added laptop sleeve. My body will provide decent shock isolation, at least until I burn off all this excess fuel.
If I had a long daily commute I think I'd be more in favor of panniers, but right now I'm thinking more in student mode - run a series of errands around town (max 8 miles across town), go out to the coffee shop to meet contacts, work on my resume and standards, and network. Panniers are as said hard to carry around indoors. Possibly the Arkel briefcase would be better than say my Madden pack.
A final note on vibration and shock: From an electronics engineer's point of view, it's better with sizable electronic products (like a laptop) and single devices (like a laptop screen) to avoid shock and vibration altogether. Small products like PDAs and cell phones are less vulnerable. However, there are ways (thanks largely to the Department of Defense) to design equipment to withstand the expected shock and vibration for a reasonable useful life. In the laptop and auto industries, techniques were developed to provide durability at little additional cost. If you have a padding system in a pannier that fits your laptop well and seems to have about the same degree of isolation as a good quality laptop briefcase, I think the laptop won't be affected significantly by bike use.
But I don't expect all laptop sections or laptop sleeves to be the same. Look carefully at fit to the PC, retention, and isolation. I like that the Arkel has (at least was here reported to have) an additional layer of suspension in addition to the usual.
Last edited by Road Fan; 05-12-09 at 08:07 AM.