If you're getting an error lack this on Dreamhost while attempting to use DataMapper and MySQL:

/usr/bin/ruby1.8: relocation error: /home/username/.gem/ruby/1.8/gems/do_mysql-0.10.1/lib/do_mysql/do_mysql.so: undefined symbol: mysql_get_ssl_cipher

One way of fixing it is to remove -DHAVE_MYSQL_SSL_SET from the Makefile flags in ~/.gem/ruby/1.8/gems/do_mysql-0.10.1/ext, then do a make clean; make; make install.

(because the Internet had nothing for me and I spent three hours going down blind alleys to no avail)