I\'m creating a web app that requires registration/authentication, and I\'m considering using an email address as the sole user id. Here are what I see as the pros and cons (upd
I think you missed a PRO:
Users are likely to remember their email address; and as email addresses are unique, they never have to worry about their preferred username being taken already.
Personally, I prefer just using my email address as a username. It's one less thing to remember, and I never have to worry about my preferred name being already taken.
Just my 2 cents!
One setup you may want to consider: Have both a username and an email. The email is used to login and is always kept private, the username is used to identify the user in any public interaction, such as posting a comment. It winds up being slightly more secure as both halves of the user login credentials are kept private, whereas if you use a username for both login and public identification, half of the login is already known.
I definitely agree with you about having minimal registration for most cases, but depending on what you're doing you may want to balance that against added security for your users. Four fields isn't outrageous for registration, (username, email, password, confirm password), and if you're feeling particularly adventurous, you could cut it down to three by dropping the confirm password field, or two by emailing them a password that they can change later.
Stick to email addresses they are used everywhere, actually most of the major websites use them, they are unique so they save the user from struggling to find a name that's not used by others, also users won't forget their email addresses (in most cases at least :)), which is unlike usernames that they will keep on forgetting if they don't visit your site very often.
You shouldn't be worried about them being too long as all the major browsers (IE, FF .. etc) offer autocomplete to forms which is enabled by default, so you type the first letters in your email and you get a drop down list (ie. autocomplete list) where you just click to enter the whole email, personally I almost never type the email address in full, I always type the first letters then select the email from the autocomplete drop down list. Besides, if you allow users to be remembered (using a Remember Me checkbox and persistent cookies), it will be another reason to not worry about it.
I don't know about your app but usually users having multiple accounts is not desirable in most apps.
CON: Not everyone has an e-mail address. Consider if your database is ever accessed by an internal application. If you are running a store, people will call up and place an order by phone and refuse to provide an e-mail address. So while having an e-mail address as the default user ID is cool, be sure to allow alternates to get into the system. (Of course, this depends on the context.)
Learned this one the hard way.
I tend to not prefer pro/con lists, and instead try to think of benefits and challenges.
Challenge:
Some users will be tempted to use their email address from their ISP. Linking to an email alone, may be difficult for the users who forget to update their email in all the web sites they have signed up for before they change ISPs.
Instead:
You should consider allowing a user to provide multiple addresses, as well user-selected id and then let the user decide what they want they wish to do. Perhaps also consider allowing the user to provide an OpenID account.