I completed an upgrade of Debian Lenny to Squeeze on a production database server over the weekend. It went quite well and I had zero downtime thanks to my secondary database servers running in-place. One of the biggest benefits to running Squeeze is that MySQL runs at version 5.1.49. Lenny only supports up to MySQL 5.0.
Row-based-replication is safer to replicate data to other servers since all changes are replicated. Prior to MySQL 5.1.14, updates to the mySQL database were not replicated. They were updated via statements (e.g. GRANT, REVOKE). This can potentially cause data-consistency between the master and slave servers, if one runs a INSERT and SELECT (w/o ORDER BY) as the order of the results will be different. If you had a SQL statement on the MySQL database that ends up erroring out, your slave connection to the master server would stop.