You can upgrade from any v3.x-x to the latest version (currently 3.3-4). We have recently upgraded 3.0 and 3.2 sites. Content can be an issue with 3.0.x sites but there are not too many issues with v3.2-x sites. You will need to take the live sites to your dev environment and then upgraded test etc, but thats standard practice, so you should be ok.
-- tony
Tony Wood : twitter.com/tonywood
Vision with Technology
Experts in eZ Publish consulting & development