Uxrae: You've heard right, and it's in GCC's website. They've been reported up to 25% speed up compiling C++ code without optimisations and the main changes for 4.x.x are Tree SSA (which would help to improve code optimisation) and a new and faster hand-written parser (C++ only for 4.0.x, C for 4.1.x).
What I'm really waiting for is the 4.1.x series (4.1.0 should be released soon) but I bet the first ones will be really buggy.
So, even when it's almost getting off-topic, I recommend using GCC 3.4.3 in the meanwhile (I had some problems with 3.4.4 because of some undefined references, and the workaround wasn't that helpful).
BTW, GCC 3.4.5 could be released soon too (at least I got that one in my Linux box as a pre-release).