According to this, Microsoft has decided to name Mango update as Windows Phone 7.5, which signifies that there are enough new features which compel them to do so. This includes better integration of applications + improvement in Live Tiles, Application Market, access to motion censors and camera etc. amongst others.

Hopefully these updates will bring WP onpar with iOS + Android in most areas. Personally I think WP has the best interface of these three (well Google copied iOS's appearances so I think there are only two genuine interfaces out of these). And with newer generation WP devices coming out once this update is launched I believe I'll be ready to get rid of my SGS