Here's what Blogger has to say about the situation:
What happens when team blogs switch to Blogger in beta?
A team blog will only switch to Blogger in beta when the original owner moves his or her account over.
Team members who have not yet switched to Blogger in beta will still see the blog on their dashboards, but it will be grayed out and inaccessible. Once those members move their own accounts to the beta, they will be able to access the blog as before. If they can't yet switch, or don't wish to, they can ask the owner of the blog for a new invitation to join the blog on the beta version. They can then accept that invitation by logging in to or creating a Google Account to post to that blog. (Later on, when they do switch their Blogger account to the new version, they'll have an option to merge it with this account.)
If a team member of a blog switches their account to beta before the blog owner does, then the team blog is not converted. It will appear on the team member's dashboard in beta, but clicking on it will lead back to the old version of Blogger. Thus, the blog will still be usable, but without the new features of Blogger in beta (e.g. Labels, Layouts, etc.).
How do I switch to Blogger in beta?
Thanks for your interest in all the new features we've got coming up! The Blogger in beta program is going to start out small, so only a low percentage of people who log in to Blogger will see the option to switch over. If you're one of them, you'll see a blue box in the sidebar of your dashboard highlighting the new Blogger in beta. Click the "learn more" link there and we'll walk you through the process of switching your account.
Part of this change involves converting your Blogger account into a Google Account (learn more about Google Accounts). If you already have a Google Account, log in with your Google Account email address and password when prompted. A confirmation message will appear to indicate success.
If you do not have a Google Account, you will be given the option to create one. Your new Google Account will automatically be linked to your Blogger account.
Blogger has a new Terms of Service so be sure to read and accept it when it is presented.
That's all there is to it. From this point on, you'll log in to beta.blogger.com, instead of the usual www.blogger.com, to access your account's new features. Remember also to use your new Google Account login information.
If you don't have the link on your dashboard, don't despair. We'll be adding more and more people as we go along, so eventually everyone will be able to switch.
Never mind. I'm just going to send you all new invitations so you don't have to wait.
Why the change? Well, besides the cool new features and the fact that IT'S! NEW! AND! SHINY!, Blogger explains that:
Google Accounts are better protected against fraud, impersonation, and abuse. In addition, by switching your Blogger account to a Google Account, it will be easier to use other Google services like AdWords, Google Groups, Google Alerts, Froogle Shopping List, Personalized Search, your Personalized Homepage, Google Answers, and many future Google services. You can find out more about Google Accounts at the Google Accounts FAQ.
I'm so sorry about all of this... I should have read the fine print before switching my personal site over. If you have any problems with the changes, please let Jacq know. Kidding. I'll do all I can to make this transition as smooth as possible for all of you. Call me or email me and we'll figure it out!