Sarah nice job on finding the links here are both my post from the links Sarah provided
I like pen blades, on my peanut I use it when whittling, opening things, trimming fishing line and save the clip for food or gutting fish. I find it to be a good all purpose blade, strong point and some belly, I find on Jacks I use it more than the main blade.
I tend to use my pen blade for most task, like Steve it is the blade I use most for carving, short blade close to what you are working on for control, strong tip and some belly. I use it to sharpen pencils, as a scribe ( unless I have a awl ) cutting string, fishing line, scraping, pretty much what everyone has stated above, but I keep both blades sharp, just a slightly steeper angle to the edge.
In addition I use it as a scraper so the main blade remains sharp, it makes a good general purpose utility blade, I recently picked up a Case Eisenhower cheap to throw in my left pocket, and use basically as a general EDC utility, partly because as a boy I had a Case 6201 that I used for everything and it's pretty small, smaller than a peanut, I still have it and it survived everything I through at it as a kid minus the bail that I lost along the way, and I used it pretty ruff in my youth.
Pete