Brad points out some UX problems with a variety of apps that are doing things a little outside of the norm when it comes to their login forms. There is already a bunch of things to get right with forms to begin with (e.g. use the right input types, label your inputs, don’t have whack password requirements, use SSL, etc.)… OMG why complicate it even more?!
A “password manager test” should be a development best practice here. Does it work cleanly with the built-in browser password manager? How about 1Password and LastPass? No? Give it some love, please and thank you.
Another point not mentioned there is to avoid using labels that look like placeholders (e.g. inside the field) until they’re focused. This can be made to work in all browsers, but Chrome has a major bug: if the field is auto-filled by its password manager, until the user takes an action on the page (such as moving focus to the page), there is no way to detect if the fields have content.