I've just finished a long saga trying to get an Arduino Ethernet to talk to me.
Small sketches, flash a led or whatever, ran fine; anything involving the
Ethernet library (my reason for getting the Arduino) sometimes worked and
mostly failed.
I installed a copy of Ubuntu, which had a very old avr-gcc as part of its package,
and that worked, but nothing I did could get my own system to program the
Arduino correctly.
I spent several days trying to get GCC 4.6.2 to compile, which had another
set of problems, and finally got binaries of avr-gcc-4.5.1 from avrfreaks. They
worked (with Arduino-1.0.1-rc2) and I had solid Telnet and HTTP connections.
Reverting (by accident) to the 4.5.3 avr-gcc brought the flakiness back, and
had me cursing for most of the twenty minutes it took me to find my mistake.
So this is a warning - probably not all versions of the 4.5.3 cross-compiler are
off, but it's definitely a version to avoid, particularly when starting out, when
it's difficult to know whether problems are hardware, software, or PEBKAC.
Will