I've added the ability to safely replace selected global symbols with constant values (which can then allow the minifier to collapse entire sections, like #ifdef in C++) which has been pulled into the main tree, and the ability to spot and shortcut constant expressions involving &&, ||, and ?: (ie eliminate the RHS when a true constant value on the LHS means that the RHS will never be evaluated).
I've also added the ability to mangle selected object property names, which obviously needs some care, but is great for obfuscating internals and can shorten long method names etc. This change is only in my fork for now - https://github.com/schmerg/UglifyJS (see the mangleprops branch)
Anyway - I'll post things to github as I go...