MySQL | MySQL dropping BDB support
According to the changelog for the 5.1.12 beta release:
Incompatible change: Support for the BerkeleyDB (BDB) engine has been dropped from this release. Any existing tables that are in BDB format will not be readable from within MySQL from 5.1.12 or newer. You should convert your tables to another storage engine before upgrading to 5.1.12.
I presume this won't hurt too many people - I've yet to hear of anyone using BDB tables, though I bet there might be some older installations from pre-InnoDB days around - but it should be interesting to watch out for further developments of this nature.