Wow, that's great news Rothgar!
We're still using the UIBuilder from 2005, version 1.3.0.0, and been complaining about it for at least that long.
Maybe you could put the updated things on the test server when test update 40 goes there. I don't think anyone else can give out beta information or files without breaking the NDA.
I think my biggest complaint is that there isn't a way to just save one file, so the UIBuilder just saves a huge number of files that you don't want it to making a huge mess. Currently I do all my editing with Notepad++ and only use the UIBuilder to visualize things, test some scripts, and double check links between objects.
The other bug that used to hit me was when using the image SourceRect selection window it would often blue screen crash my computer. I've been really careful with it so it hasn't happened recently.
I always send /bug reports for any UI bugs that I find. If you don't have all those already I'm sure we can put together a list for you. I guess it gets a little disheartening to report bugs all the time and wait months or years and never see them fixed.