I've never really minded the New York Times login. I only do it once a browser and the content is good enough it's OK. But yesterday I went to login and was told "we've changed our system and your login nelson@santafe is no longer valid". To their credit, they did have an easy path for changing my login, but why the change at all? Who decided email addresses weren't valid logins?
My biggest problem with all the sites I log into is remembering my username. It has to be unique, but different sites have different restrictions. Am I Nelson (not unique), or NelsonM (ugly), or NelsonMinar (too long for some), or firstname.lastname@example.org (contains punctuation), or email@example.com (plus is often not accepted)? By contrast I can usually use the same low security password on all these sites, because passwords have fewer restrictions and don't have to be unique.