Blogger Dynamic Views for Google Chrome lets you toggle blog designs while browsing
The extension adds an orange Blogger icon in your address bar when you're visiting a Blogger blog. If you click on the orange icon, you'll get a list of the five aforementioned Dynamic Views. You can then select an option and Chrome will render the blog you're visiting using that particular view. Rinse and repeat if needed.
Naturally, you can still access the new Dynamic Views (in any 'modern' browser) just by appending /view to the URL of the blog you want to visit, however the Chrome extension makes it a lot easier to get to the new layouts.
Download Blogger Dynamic Views from the Google Chrome extension gallery