I'm not linking the Skin part of Flash Builder for Spark components. It is really hard to set a new skin for a new component. Moreover there is no such CSS design mode which allow us to easily embed our Skins from either Flash or Image. I'm creating a small application which just has 8 forms and it took me 3 full days to Skin those...this is bad. Earlier in Flex 3 it was just 1 day job for me.
Adobe please do something I do not see Flash Builder as Rapid Application Development tool at all. In fact most of you also agree to what I'm saying.