Check here for the changes in v2.3. Check this link as it gives all the details you'll need plus check the link (on the following page) to the Wordpress upgrade preflight checker......
http://codex.wordpress.org/Version_2.3
There's been some changes to the db structure which could have a big impact...
http://codex.wordpress.org/index.php...3:New_Taxonomy
Gonna have to take the plunge eventually, I think I should let the client see the website completed before suggesting the upgrade, at least he will know that it DID work before I go and break it!