I've got a couple of outboard brains. This weblog is one of them, but I also use an app on my PowerBook to store stuff that I don't necessary want Google to find (passwords, source code snippets that don't make sense out of context, list of the members of the Illuminati, etc...)
I'd been using DevonThink PE as that "private outboard brain". It works really well, and handles all kinds of file formats (as well as web pages). I just switched to Notational Velocity, though. At first I didn't get it. I thought NV was a gimmicky app that I wouldn't find useful. However, after a bit of use, it's turned into a LaunchBar/Quiicksilver for data. One part wiki, one part fulltext index, one part note taker. Very cool.
NV doesn't do other file formats - it's just the text, ma'am. But you know what, that's ok... I thought I'd be using the multiple file formats of DevonThink a lot, but 99% of my notes were text anyway (with a few web pages in there, which could just as well have been converted to text)...
Just beware the somewhat disturbing photo on the NV website. Damien is apparently back, and he's writing really cool software...