BoltWire 2.0 to 3.0 Transition
After more than 70 releases, lot's of hard work went into the 3.xx release. And fortunately, virtually all the changes between 2.xx and 3.xx were introduced in the end of the 2.xx cycle, so upgrading from 2.73 to 3.xx should be relatively painless. The real work was done before the transition. :)
If you are not using the latest 2.xx release, you will want to read the release history carefully for indications of potential upgrade problems before switching to 3.xx.