Edit: this answer is outdated. PyMongo now officially supports Python 3.
The answer was already given in comments, but I'll provide a comprehensive summary nontheless:
- As of May 2011, Python 3 is not officially supported by MongoDB
- Ticket for "Support for Python 3" has been some years ago (https://jira.mongodb.org/browse/PYTHON-84) so the MongoDB developers are aware of this need.
- As already told by Adam, there is a port of PyMongo for Python 3 in PyPi (http://pypi.python.org/pypi/pymongo3) which could be used and is defined as "semi-official"
- Source codes for the Python 3 fork are available at https://github.com/sovnarkom/mongo-python3-driver
- If you want make on impact on making this fork official make an upvote to its ticket (https://jira.mongodb.org/browse/PYTHON-84)
- With enough upvotes/user requests, I would expect to get an official Python 3 driver someday
