When someone subscribes and it goes to the :
You have successfully subscribed to this list. "
Id like to remove the feature "Click here to return to the site."
For each list, under 'create a subscribe form' you can optionally define a URL that people will be sent to after they subscribe. If you put your own page there, you can have it worded exactly as you like.
We don't have a way to modify the generic confirmation page though.