If you are still concerned about upgrading to WordPress 2.1 fearing your favorite wordpress plugins might not work, Lorelle has a post which inspires you to upgrade.
She says that WordPress developers have added a backwards compatibility file to help most older WordPress Plugins and WordPress Themes continue to work. The new deprecated.php file (found under /wp-includes) in the WordPress 2.1 download adds backwards compatibility to WordPress, instructing the programming language and WordPress Plugins that the template tags were this and now are that. Lorelle has written another brilliant article about WordPress 2.1 at the Blog Herald.
It is advisable to check the WordPress Plugin compatibility list to make sure your WordPress Plugins will be working. Technosailor writes about the 10 Things You should Know About WordPress 2.1 and then points to some WordPress 2.1 upgrade issues he encountered like buggy blogrolls and absent posts.
Remember bugs will always be reported as more users try out any new version, and WordPress 2.1.1 may be out soon. See WordPress 2.1.1 under development at WordPress Trac.