It hasn't been too big of a deal up until this point since the XNA API hasn't had many breaking changes from XNA 2 through XNA 3.1 but with the upcoming release of XNA 4, there are many breaking changes to the XNA API. Many of these have been driven by the
Windows Phone work of the XNA team. What's interesting is that a lot of the changes that they are making would have actually made SilverSprite easier to develop. I can clearly see why they are making some of the changes that they are making because I
had the same pain points in many cases that they must have had.
Going forward, SilverSprite will align itself with the "Reach" profile of XNA 4 wherever possible. There will still be no support for 3D but we'll try to support as much of the rest of it as we can. Some details on what is in "Reach":
I also highly recommend subscribing to Shawn Hargreaves' blog for details on breaking changes in XNA 4 and a lot of other useful info.