If you visit the Froogle Merchant Center you will see this message posted on the left hand side of the page.
In case you've been wondering, the old Froogle Merchant Center has been replaced by Google Base. Your existing account information and bulk uploads (formerly known as 'product feeds'') are already viewable there, and you can continue to upload your product data just as you did before.
There is a whole Froogle Migration documentation section to learn more.
Where did the Froogle Merchant Center go?
The Google Base dashboard has replaced the Froogle Merchant Center. Your existing account and product information have already been transferred and are now viewable in your new Google Base account. From now on, when you click "Information for Sellers" on the Froogle homepage, you’ll be brought to a new sign-in page.
As well as on Froogle, your content should be viewable at http://base.google.com; you can search there to verify that your products have appeared online after you post them.
If you are looking for a good summary, check out eWhisper's post.