My most recent attempt has been a pile of Markdown files in a Github repository. I edit them directly in Github's editor and they are automatically rendered by Github, so I get nice syntax highlighting and working links. It has the added advantage that I can send people links to whatever I'm struggling with, like "Here's the error message I'm getting: ."
Here's my log: https://github.com/pingswept/dev-log (Obviously, this only works because most of what I do these days is open source, but it could work just as well on an intranet.)
I've been creating a new file for each day's log, but I think that might not be quite the right approach. It makes searching a little more difficult (though still much easier than notebooks), but makes editing easier because I don't have to scroll to the bottom of a huge file to start typing.
If anyone has suggestions of better ways to do this, I'm definitely interested.
(Hmmm. Maybe there's a keyboard shortcut for skip-to-bottom-of-file in the Github editor. Edit: hey, there is! Command-down-arrow.)