I've seen this little challenge bobbing around the blogosphere quite a bit over the last few days, and I originally saw it on Vicki Thompson's blog The View Outside. This is an excellent blog by the way, it really keeps me going with a positive feeling towards my writing when I read Vicki's posts, so thanks very much to her.
The idea came from Jerry Seinfeld and if you want to download the calendar for free then click the link here.
I actually had a little trouble printing this off myself so I've made my own, but the principle is the same.
Have a go, I've only been doing mine for a few days and already I don't want to miss a day. I'll post an update with my progress at the end of the month.