A weblog is an augmented memory for those fleeting moments of life where you really wish you had some record of, and where you know that if you don't write it down now it'll be gone forever. It's the capture place for that initial review of a piece of software you might or might not grow fond of, the record of what was talked about at a particularly interesting lunch meeting, or the color of a late spring sky (grey, with low clouds; good strawberry picking weather if the rain holds off, but not good for ripening the strawberries). When you go back to reread what's been written down, some part of the memories come back. If you're lucky and captured some particularly salient point, the entire memory – the entire conversation – can return and you'll be transported back to another time and place.
A weblog is also a place for the things that you figure out through dogged attention to some terribly inconvenient detail of something that's not working. When you figure it out, you want to write it up so that you can repeat the process if it ever happens to you again. You'd really rather never have to go through the ordeal again but just in case someone else happens on it you'll have that capsule of hard-won knowlege written down. You'll write it down so that you can forget it except when you need to refer to it again, when you'll relearn it as from new based on your old notes.
I'll cheat from time to time, going through old posts and updating them with new information or with recollections that match the time. Every so often I'll unpublish a piece that sounds like it doesn't want to be something that I want to remember and that isn't forgotten yet, or that has such atrocious grammar that I don't want to be remembered by it. My drafts folder has over 200 such articles, ones that neither qualified for remembering or for forgetting, but that I can't easily bring myself to completely deleting.
Some blog to remember, some blog to forget (apologies to the Eagles).