Most of the plugins are compatible with WP 2.7 but just in case I'm suggesting you to backup you db and files, the migration process is pretty simple and won't take any special efforts, AFAIK you are one-click away from upgrading.
There is a new function of hiearchy which can be implemented in the templates but it's not a must/mandatory and your blog will be just fine without it.
Other than that I personallry didn't upgrade my blogs though due to the fact that I don't have time to backup everything before migrating
