What sort of things do you put in them? I don't know about you, but I'm not exactly running experiments. Do you have a format that differs from purpose, procedure, results?
I'll start with the date and a big horizontal line.
For meetings I'll put the start time and a quick header, then some quick notes, usually not even complete sentences, I'm just scribbling things down to remember.
In deep coding, debugging, or infrastructure stuff: I'll keep short notes on infrastructure stuff, URLs, hostnames, ports, function names, file names, lots of breadcrumbs basically. This is often great the next day, where I might not really remember how I got from A to B, but all of a sudden need to make a document describing it for other people to repeat. This is the part that is most like a "lab notebook."
If I'm designing something new or exploring something, I'll often sketch system diagrams or the like. I'll maybe try to diagram flow between components, user steps, basic algorithm steps, etc. Think design document, version -1.
I'll often intersperse TODOs as well, which I'll try to quickly migrate to something real (Jira here at work, or my iPhone tasks list.) I don't use it for task tracking, although I used to do that.
