The website, http://www.nltk.org, says mid 2011 in a very vague manner. I would like to start using NLTK however I have done a fair amount of work with Python 3.x and I don
There's a Python 3 branch:
https://github.com/nltk/nltk/tree/nltk-py3k
It's a transformation of the trunk and gets updated every so often to keep up with changes. You can check it out directly from git (instead of using the NLTK installation) and give it a shot.
git clone git://github.com/nltk/nltk.git nltk --branch nltk-py3k
I haven't used it personally, but I assume it works.