The latest nightly build of Chimera now uses Command-arrow navigation for back and forward! This was the biggest thing killing my buzz about Chimera but it is fixed now, so go get it! Get it here:
http://ftp.mozilla.org/pub/chimera/nightly/latest/
Note that these nightly builds are not in any way guaranteed to be stable, but the Oct 3rd build feels pretty solid.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2002100905375792