Today I downloaded the TDM distribution of gcc 4.5 for Windows and played around with it a bit. Part of that playing around including cursory checks to see what new features of C++0x were supported, and I was pleased to see that there were quite a few, including lambdas, raw string literals, and new STL algorithms like all_of/any_of/none_of. I updated my summary of C++0x feature availability with the new information, and as long as I was at it, I also added a link to C++0x support in Clang, as I'd happened across that page a couple of days ago.
Gcc 4.4 already had a lot of C++0x support, and in conjunction with MSVC 10, which also offers many C++0x features, it was already possible to experiment with lots of C++0x, but with the introduction of gcc 4.5, not only do we have even more of C++0x to play with, but, thanks to gcc's support for lambdas, writing portable C++0x code is now easier than ever.
If you find the revised C++0x feature availability table useful, please spread the word about it. If you find errors in it, please let me know about them. Either way, have fun with C++0x!
Scott
PS - Even if you're familiar with Gnu's summary of C++0x support in gcc 4.5, you might want to take a look at my table, because Gnu and I break things down differently. Gnu's table, for example, makes no mention of alignof, but my table includes it as a line item, which is why I was motivated to see if gcc 4.5 supports it. It does!