I don't think it used to? I remember needing to explicitly state tar -xjf for bz2 stuff. I do it now reflexively. If it's handled correctly by -xf, that's awesome!
Yes, it does, but only GNU tar. I was using NetBSD when I stumbled over the fact that it couldn't 'tar xvf' my foo.tar.gz.
OTOH, I always have to look up unzip, because I fear that there is some option that I forgot. Well, most of the time I use a GUI for Zip, since they often decompress all over the folder unlike tars which are mostly contained in one single folder.
