Version 4.1.22 contains a prodigious number of bug fixes. It's also worth noting that active development and support, for this and some other versions, has ended. There's still extended support available for MySQL 4.0 and 4.1, though, and you can get all the details on that, here.

In addition, only Security and Severity Level 1 issues will still be fixed for versions 4.0 and 4.1; so you really ought to consider upgrading to MySQL 5.0 or 5.1. Meantime, here are some highlights of this version's bug fixes:

• The value of --table-open-cache is no longer increased automatically, and a warning is now given only if some values had to be decreased due to operating system limits. 
• A warning is now issued if the client attempts to set the sql_log_off variable without the SUPER privilege.
• A problem in the code that handles internal temporary tables has been addressed so that it no longer leads to writing beyond allocated space and memory corruption  under heavy load (defined as executing more than 1024 simultaneous complex queries).

For details on all this version's fixes, please read the information you'll find here.