Great pattern -- I'd like to see it include an additional guideline. Not only should you "return them to the context they were in when they were about to comment" but take additional steps to preserve this context even if there are problems during the sign-in process. I've seen plenty of apps that get the first part right, but assume a seamless, error-free login. Then they have some semi-hard-coded "Return to top of site" behavior as a generic catchall action from the Sign-in Error page. T-mobile, I'm looking in your direction…
-- Bryce



