If you'd like a sample of how do to that, check out the scripts Alfred & I worked on. We used imagemagik for changing the lock screen to include weather and such. (I still use this as well.)

Currently I've having an issue with the QBW script, in that after a while QBW stops calling the script on close events. I updated the script to change it's timeout via dbus, which seems to be semi-broken and is probably the cause of it breaking after 10 or so hours of use.

If I get that stable, I'll post the widget and script again. I may eventually bite the bullet and see about creating an honest app out of it in C, since it seems like a good/small project to get into the devel stuff with, which I've been wanting to do for a while (and may actually have some time for in the near future.)