I am a proud member of /r/trebuchetmemes and /r/arcticmonkeys. My santa knew his way around and he got me some treats, a miniature trebuchet and an trebuchet/arctic monkeys/dungeon keeper (yeah I saw that in the corner) themed postcard with catapult and cars2 targets for practice. The card is a windows wallpaper masterpiece.

I got it working in about 2 hours. I can confirm that it can launch an 20g (~0.7oz) tinfoil + clay projectile over 5 meters (~16.4 ft) so it exceeds the extrapolated values!

It was very fun project, now it's sitting on the top of my bookshelf for display.