I'm quite intrigued and really wonder how will it evolve. To date, their site is not really useful for discovering new cool stuff, but I think they don't really want to be a source of cool stuff; there are lots of sites already dedicated to that (digg, stumbleupon et al). Instead, I believe they are focusing on making sure there's a flattr button in every post, picture, software and etcetera, so that you can thank/show your appreciation to their creators.
Paying homage to my ancient Catalan roots, I've decided to install the Wordpress plug-in so that you can flattr my stuff in case you want to. I guess it may come in handy for cases such as the DIY tutorial for replacing the mac mini hard drive: lots of people liked it and some even asked for a donation button, but once I placed it, very few of them actually did donate. Probably because PayPal is a bit of a hassle, or maybe because making people decide how much to donate, entering their user name, password, etc... was just too much. Now with flattr it should be easier. Let's see :-)
Oh and I just found out I have
three two flattr invites. So if you want one, let me know.