I did another clean install on a different server with 3.3-3 and the shop package. The checkout button redirects by default to /shop/user/login (where /shop/ is the site interface). On a clean install of 3.3-2 the checkout redirects to /shop/userregister/ (where /shop/ is the module name). I think it's a bug, but it could be the correct behavior as well from 3.3-3. I guess I'll stick to 3.3-2 for now.
#?ini charset="iso-8859-1"?
# eZ publish configuration file.
#
# NOTE: It is not recommended to edit this files directly, instead
# a file in override should be created for setting the
# values that is required for your site. Either create
# a file called settings/override/shopaccount.ini.append or
# settings/override/shopaccount.ini.append.php for more security
# in non-virtualhost modes (the .php file may already be present
# and can be used for this purpose).
[HandlerSettings]
# A list of directories to search for shopaccount handlers
Repositories[]=kernel/classes
# A list of extensions which have shop account handlers
# It's common to create a settings/shopaccount.ini.append file
# in your extension and add the extension name to automatically
# get handlers from the extension when it's turned on.
ExtensionRepositories[]
# Settings for how user accounts should be handled in the shop/checkout
# default is to use internal user accounts in the system
# simple is for handling account information without user registration
[AccountSettings]
Handler=ezsimple
#Handler=ezdefault
# Allows for overriding a handler with another
Alias[]
# Alias[ezdefault]=eztest