I've been using it since 4.3.0Dev and 4.3.0RC2 and 4.3.0RC4.
I think my favorite little feature is the -r switch for the command line.
$ php -r 'print $_ENV['SHELL'];'
Thought this new feature was in 4.3.0Dev and 4.3.0RC2, I didn't see it in 4.3.0RC4... I hope they didn't get rid of it!