Last access time for database, table, user

When you run hosting customers create a lot of databases and mysql users over time and never delete them (as they like to limit themselfs to deleting only files via ftp). For cleanup purposes It would be nice if you could on-demand enable/disable gathering statistics like last access time for database and last access time for mysql user. Last access time for tables is less important here but might be usefull in other scenarios. It might be enought just to make general query log without queries (only connections, inits).