From now until the end of the year, you can earn 1000 XP for _each_ new WP8 app or game, and an additional 1000 XP for _each_ existing WP7 app or game updated to WP8!
For some perspective: 750 XP will get you a $50 Amazon or Starbucks gift card, or a year of Xbox Live. There are a bunch of other great rewards you can earn - check them out here.
There's more information at the official Pointstravaganza blog post. If you're planning on working on an app, drop me a line - I'd be happy to help or test or whatever I can do!