Is there less or more plugin support with 3.0?
This is a very subjective question because this is based on which plugins you are using. Generally I think there are more plugins available for 2.9.x or even 2.8.x but these numbers might be just misleading.
If you have not modified your blog at large so far and your theme and plugins are compatible with wordpress 3.0, you can consider upgrading. Do a backup first so you can go back in case something breaks.
My 2 cents.