I recently noticed that after switching over 2 of my blogs to the Blogger Beta that i now have the option to "upgrade the template" but it does warn of the following: "We've introduced a new tool for customizing the appearance of your blog. Before you can use this tool, you'll need to upgrade your template. By upgrading, you will lose many of the changes you previously made to your template. However, we will save a copy of your current template so that you can access it later." Im curious if anyone has upgraded their template this way and possibly wished they had not, did it cause you such problems as to really mess up your blog or was it mostly a case of a bit of rearraging after going ahead with the template upgrade?
I've upgraded, and its been fine...you do have to tweak your template if you made serious alterations to your old template. Anyway, theres a link at the bottom of the HTML template section to revert back to your classic template if you wish to do so.
I have upgraded my template but not much lost any data. Just change some arrangements. Also re-verify your site from Google sitemap by adding your meta tags there.