Like most Apple updates, we suspect that the new beta 3 includes several stability and performance enhancements that might make the beta more pleasing to use, if you are testing it.
We've heard from some early beta testers complaining (see article comments) about the number of issues they were experiencing with the previous releases.
It is too early to tell what kinds of changes have been made in beta 3, but we suspect that it will not take long for people to discover them.
World of Apple has republished the seed notes for the iPhone Beta 3 SDK, listing changes made to various components, such as Xcode, Interface Builder, and Dashcode.
Developers and beta testers, let us know about your experiences with this latest iPhone OS 3.0 beta in the comments.