Even though said support is labeled as experimental and is not activated by default (-std=c++0x in the command line does the trick), GCC 4.4.0 seems to be working just fine. Or I should rather say that Zero seems to be debugging GCC 4.4.0-generated code just fine.
I have installed the latest compiler snapshot on a Ubuntu 8.04 beta system, by simply typing apt-get install gcc-snapshot (apt is the awesomest).
Then I set the compiler to /usr/lib/gcc-snapshot/bin/g++ in my environment and fired up a battery of automated tests.
I also did a bit of manual testing for variadic templates, using code samples straight out of Wikipedia, and one quick test for rvalue references. Things look good so far.
Surprisingly, all unit tests having to do with floating point variables passed.
I may have to look deeper into these tests, since as stated here,
"Starting from GCC 4.3.1, decimal floating point variables are aligned to their natural boundaries when they are passed on stack for i386."
I will keep you posted.