<p>Clicking through to the download-page if see that the last version of the download is <strong>over one year old</strong> and it's also "just" a <strong>Release Candidate</strong> of version 1.0. There are really no news on any development.</p>

<p>Yes, you can find newer versions from the nightly builds, but that's not a real serious option.</p>

<p>Also, the "getting-started" and description-pages are sometimes not even started and some not completed.</p>

<p>What's the deal? Any C# 3.0 features on the way or what?</p>

I'd suggest PNG. Most software supports writing it, most libraries support reading it, it's lossless and supports alpha transparency. And it's a standard format.
And, maybe important for hobbyist 2D games, very small images also result in very small files (i.e. a 16x16 icon can be 1KB or less).