I’ve found a site that I want to print out and leave at everyone’s desks at work: notaverb.com. It makes the case conclusively that “login” is not a verb (if you don’t want to read the page, use it as two words). This makes me unreasonable happy–as does the conclusion on the “login” page:
If you take only one thing away from this page, take that one fact: “login” is not a verb. Educate others. Correct manuals, software, and web pages as you find them. Tell everyone you know that “login” is not a verb. You will make a pedant (me) happy. You will earn the respect of grammar nazis. Most importantly, you will know the truth.