Handling money requires a stable and trusted service which is why it would have been a bad idea not having a closed beta to test it out properly before released. The problem with handling money is that there is a lot of legal issues around it.
@cabalamat there is already an API that community has used to create a lot of cool stuff with: https://flattr.com/support/plugins Hoping to see many more though so if you have good ideas feel free to hack away:) Donating specific sums can already be done to other Flattr users via their profile page.
We're actively working on getting Flattr more accessible and available to "flattr everything". Big changes happening in a few days! http://blog.flattr.net/2011/04/flattr-reloads-the-cannons/
/josef (@flattr_intern)