I put my laptop in a simple laptop bag.. just a compartment for the unit.. and drop that in my large pannier and I surround it with dense foam pieces I pulled out of a shipping box some stuff came in. The foam pieces weigh next to nothing,but do take up space. But no biggie since I use other bags for the other stuff.

I've only done it once and in fact I'm typing from the destination with no ill effects.

+1 The only difference is that I have the large Ortlieb Office bag. Waterproof and durable.

I use a laptop backpack, but I think it's not the best for commuting in hot weather. If you have a commute longer than 3 miles, your back will be drenched. If it's short like mine... not a problem.

For longer commutes, I would suggest what others have above... rack, pannier and laptop sleeve.

--sam

+2 - it's perfect

I carried mine on my back in a T2 messnger bag for years. I realized it was huge mistake the first day I rode with the Arkel commuter. I'll never go back.

NOT on your back, a suspended sleeve inside a good pannier.

When I carry my laptop I put it in a laptop backpack, then put that backpack inside my grocery pannier... rides nice, lots of cushion, never had a problem with it.

:)