The state of logins is horrendous. With each site having it's own rules for passwords, it can be very hard to remember what variation you used on any given site. Logins are pure pain. One thing I love about Craigslist is that it did away with logins altogether. I know this design may not suit every site, but there's something to their design that beckons to be repeated.

OpenID is great on sites that have adopted it, but it's still not standard.

Would it be feasible/wise to use an email address as a login and provide no password? The site would send a short-term key directly to your email address. You click on the link and you're in. When you're done, you "logout" and your key is terminated.

I've toyed with this idea before. What concerns (i.e. spammers, bots, etc.) would make this impractical or unsafe and could they be overcome?