MySQL fails after upgrade to 5.1 on Debian Squeeze

Are you running Debian Squeeze?
Did you upgrade to mysql-server-5.1 ?
Are you getting a message like this?

Starting MySQL database server: mysqld . . . . . . . . . . . . . . failed!

Did you read /usr/share/doc/mysql-server-5.1/README.Debian.gz ?
Go read it again and this time *comment out* skip-bdb in /etc/mysql/my.cnf:
perl -i.bak -pe 's/^(skip-bdb)/#$1/' /etc/mysql/my.cnf