The idea of using a blogging platform for your lab notebook is pretty simple and the advantages are numerous. All your entries are automatically dated appear chronologically. You can view your notebook or make new entries from anywhere in the world. You can copy and paste useful code snippets, upload images and documents, and take advantages of tags and search features present with most blogging platforms. I keep my lab notebook private - search engines can't index it, and I have to give someone permission to view before they can see it. Once you've allowed someone to view your blog/notebook, you can also allow them to comment on posts. This is a great way for my mentor to keep track of result and make suggestions. And I can't count how many times I've gone back to an older notebook entry to view the code that I used to do something quickly in R or PLINK but didn't bother to save anywhere else.
Of course Blogger isn't the only platform that can do this, although it's free and one of the easiest to get set up, especially if you already have a Google account. Wordpress is very similar, and has tons of themes. You can find lots of comparisons between the two online. If you have your own web host, you can install the open-source version of Wordpress on your own host, for added security and access control (see this explanation of the differences between Wordpress.com and Wordpress.org).
Another note-taking platform I've been using recently is Evernote. Lifehacker blog has a great overview of Evernote's features. It runs as a desktop application, and it syncs across all your computers, and online in a web interface also. The free account lets you sync 40MB a month, which is roughly the equivalent of 20,000 typed notes. This quota resets every month, and you start fresh at 40MB. You can also attach PDFs to a note, and link notes to URLs. Every note is full-text searchable.
And then of course there's the non-free option: Microsoft OneNote. Although it will set you back a few bucks, it integrates very nicely with many features on your Windows machine. I've never used OneNote.