MichaelMeissner:
For example, on Linux (Fedora) if I install the arduino software via the yum repository, compiler is fairly new (4.6-ish), while if I use the compiler that is supplied with the Arduino 1.0.1 tarball, it is rather old (4.3.2) which is several years old, and 4 major revisions out of date.
I notice that the Arduino 1.5beta released yesterday also uses avr-gcc-4.3.2 for the AVR architecture, and arm-none-eabi-gcc-4.4.1 for the SAM architecture.