strcpycat – How hard can it be to write a function to copy one string to another? This exploration shows how tough it is to create an algorithm that's truly generic. Seemingly-harmless design choices like returning the length of the source string will kill you when you're copying small chunks from a massive string.
Is there life on Venus? – We believe our own eyes, even when we shouldn't. This is a cautionary tale of a respected Russian astronomer who started to see life forms in the image-processing artifacts of old space missions. I used to generate 8×8 sprites for my 80's game programming by cycling through random blocks of pixels until something caught my eye, so I'm aware of how powerful pareidolia can be.
How to digitally sign a PDF – I can't believe I never knew you could do this, I've wasted so much time printing out and rescanning documents over the last few years of startups! In Lion it's so easy, you can just write your signature on a piece of white paper and hold it up to the camera, and after that just position it in any PDF you've loaded in Preview.
IMDB data set – Emphatically not free and open, but at least available, I'm intrigued by the Kevin Bacon possibilities here.
Computer Scientists and Google+: Something Interesting is Happening – As you may have noticed, I'm optimistic about Google+'s prospects. It comes down to my personal experiences, I'm discovering a lot of content that I just don't see on Facebook or Twitter, and it looks like I'm not the only one.
Pete Warden's blog 