Our new shop finally made it and is now accessible again as usually through the menu at the left. It may be still a little bit slow, especially during checkout, but we're already working on some performance improvements. All users of the old shop can re-use their account data as we managed to migrate the accounts to the new system. Have fun and don't hesitate to contact firstname.lastname@example.org if something doesn't work as expected!
UPDATE: You may still get an SSL error when using the cart or other secured connections. This means practically no danger (as your data is still encrypted, though) and will be solved in a few days.