I see that the data sets which interests me the most aren't as useful as I would like, because they are out of date. The Genbank release is "Last Updated: December 9, 2009 2:49 AM GMT", and PubChem is "Last Modified: Jun 4, 2009 20:21 PM GMT". Both of these datasets are modified continuously.

On the plus side, Ensembl is up-to-date.