New to Netflix post will be late this week as I'm out of the country and unable to access the UK site. I can however access the US version (thanks to the marvellous 'Hola Unblocker', check it out if you haven't already) and can happily say that they've uploaded the entire first series of Adventure Time (as well as other noteworthy Cartoon Network shows). I'm hoping this is a site-wide addition but I'm not holding my breath.
If you haven't come across Adventure Time before I highly recommend you check it out. It's basically a pretty trippy kids TV show that finds humour on many other levels (such as subtle sex jokes, hypothetical drug induced hallucinations, implied violence). It's basically a way to make kid's shows fun again and has already achieved a cult-like status for many 'geeks' and 'nerds' alike.
I also recommend to check out the sister show on Cartoon Hangover's YouTube channel, Bravest Warriors.