Gizmodo and Make are both pointing to Bill Morris's DIY Cleanroom.  Compare it to the hoods shown in my post on Garage Biology in Silicon Valley a couple of days ago.

Morris reports that his goal is a Class 10,000 hood, a specification that is slightly more involved than I had remembered.

In any event, Morris' hood would be of great use to those doing cell culture at home.  I suspect you are going to want a better filter, for nabbing smaller contaminants, maybe higher airflow, and perhaps some way to hack up a laminar-flow set-up.

Cool.