Among the bug fixes is a fix that solves an issue with newer versions of the KCacheGrind profiling GUI. The newer versions are more strict with input which causes an issue with Xdebug profiler's files. Xdebug 2.1.1 solves this.
As an experiment I set up a pledge system to allow myself to work on this (and related issues) during my "work time". Twenty-four pledges were made, in about two weeks; matching the goal. Sebastian, Jan, Michael, Pale Purple, Jeff, Christoph, Karel, Yannick, Jake, Venakis, Brian, Simon, Kenneth, DM Baker, "gizmola", Ladislav, Volker, React, Michal and three anonymous supporters—thanks for your support!
Another main issue that was fixed was that line numbers (in function traces, profile files and while debugging) for "magic" function calls (such as __get(), __call() etc) were always recorded as 0. This made it impossible to set breakpoints for example.
You can find Xdebug 2.1.1's source and Windows binaries at the download page. A full ChangeLog is available as well. Through twitter you can kept up-to-date about Xdebug's development efforts and support is available through the mailinglist. If you think that Xdebug is a valuable tool, you can donate via PayPal.