Our goal with SilverSprite is to support as much as we can of the XNA API related to 2D game development. This being a part time open source project, though, we need to pick and choose what to implement since the XNA API is pretty extensive. To help us determine
the most important functionality that is currently missing I have set up a UserVoice page for SilverSprite.
So if you need a particular feature, or something isn't working right, or if you have a suggestion, please create suggestions and vote them up there.
I've been slammed for the last couple of weeks but it looks like that's going to clear up early next week so don't think I'm ignoring your discussion posts right now and I promise to catch up soon.