Kudos to Rovio for bonuses of exactly this kind - this is why we love the company. With hundreds of fan level designs sent in, in a variety of styles and degrees of sensibility, the best 30 have been implemented, for real, and placed in a special 5th BirdDay (geddit?) set of levels, ready for playing. Some of them are quite hard, too, so you'll need your best bird-flinging skills!

From the Store update description:

It’s our 5th BirdDay and we’re celebrating with our bird flinging fans! Play an all-new episode of 30 levels inspired by your fan art! We have received thousands of submissions. Now, play the levels to see the winning art. Maybe it’s your own!

Here's the new set of levels in action:

Ah, the original Angry Birds! Updated each year too, always a free update, happy times....

Ooh, look, a birthday (sorry, BirdDay) present!

Aha - 30 more levels to play, all inspired by fan art, following theme suggestions from the Rovio team!

Here's an example, based around impossible physics, ironic considering the nature of Angry Birds, but....

And here's what was sent in as a response...

In another example, this time around a space theme and hand-drawn...

...and here's what the Rovio team came up with, a pretty faithful interpretation. This is so cool...

Well done to all concerned, even if I did get stuck after half a dozen of the new levels! You can try or buy Angry Birds here in the Windows Phone Store.