I carry a lot of stuff too so I can relate. I like to be prepared in case the weather suddenly changes. Although, it doesn't really bother me. I have no intentions of making my daily cargo any lighter.
Some loose thoughts...
For portability it's hard to beat flash drives: small, no head to jam into a platter. They've gotten cheaper and faster too. But they're not perfect either. They're sensitive to EM and static electricity. I've seen flash drive lose the filesystem (appear suddenly blank) for no apparent reason. But I use them as "shuttle media" and get stuff off of them as soon as I can.
I'm not much of a Linux user but it's probably the best OS to run from a flash drive. Both Mac OSX and Windows are resource hungry behemoths while many Linux distributions are designed to run off of flash drives.
I have a netbook and I hardly ever use it: the main problem is screen resolution, many Windows programs will simply refuse to run at that resolution and, like I said, I'm not much of a Linux user. I basically use it as a glorified storage device to offload images from my camera. Since I got an iPhone I practically have no need for a laptop. iPhone 4 with the improved camera and battery life is an amazing sidekick for bike travel. With a very few exceptions, I can do almost anything on the iPhone I needed a laptop for, often even more considering the size, portability, zero boot time, built-in GPS, motion sensor and a camera. iPad is another option. I know people who mainly read PDF papers and write papers and they switched to iPads. They can write most of the paper and then edit it, add images, etc using a desktop later. Since I got an iPad I actually find myself using my desktop PC less. Majority of what I do in the evening is email and web: forums and reading articles and stories, and both work well on the iPad. Probably 25% of my recent posts here have been made from the iPad.
I carry a fleece top stuffed in a ziploc bag as someone described above. There are actually special bags for that. They allow for greater compression, have easy "air ejection" system, hold for much longer and are fiber reinforced. They're not cheap $5-10 per bag but durable. REI carries them, I forgot who makes them. I have one, but can't find it. They're great for storing backup and emergency clothing.
Adam