I'll tell you one thing that i did notice with 4L7 that was different. The finder actually remembers now that I had my last finder window open as column view, and it opens that way each time now. It did not before. Other than that, i dunno.
Actually, I'm still on 4k78 (i.e., the untainted final), and the Finder can remember stuff like this already. There's an article in Ars Technica that says that the Finder remembers window states if the tool bar is showing. I'm not to sure about that, since I haven't really been paying attention that greatly. However, all my windows have been opening up pretty consistently in column view for the past couple of days.
Well I just found out from a friend that these are builds of OS X being seeded to those in the Apple Software Seeding program. He was shocked that I had it already because he had just received it as a seeding member.
So one of the Seeding members is the one responsible for the leak.