I vote for “1.0” and not “1.3” or something, bleh! (I also advice we use a major, minor and patch level version number, “0.0.00”.) I’ve used bitcoin-1.3.0.rc3-linux[1] and found it to be mature enough to be called “1.0” in my opinion. (It was already called 1.3 there, but I guess we cal all agree it’s the next release, thus right now can be called both 1.3 and 0.3.)
[1] http://www.bitcoin.org/download/bitcoin-1.3.0.rc3-linux.tar.gz