The Go-Live FAQis still out of date though, so I thought I'd give a brief summary. In a nutshell, Go Live means that if you start using Team Foundation Beta 3 (or actually the Beta 3 Refresh) in your team, we will make it possible to you upgrade all of your data from Beta 3 to the final RTM version of the server. Support for Beta 3 is still through the regular Beta support channels.
We're currently working through the final details of the upgrade tool at the moment - it will either be baked into the Setup experience, or it will be a separate tool that you run against your server to upgrade the data to the final RTM schemas. I'm not expecting major schema changes between now and RTM, but I don't think we'll get away without making any changes, hence the need for a tool. We'll make sure that all your version control history, and work item revisions etc remain intact.
One thing that I don't expect to happen is for your methodology to be upgraded on already existing products. For example, if you go live with an MSF Agile project (or a customized version of MSF Agile), then we won't update the process guidance, work item types, etc. for that project. The methodologies would only be updated for new projects that you create after upgrading.