When a user is signing up to a new service(twitter, forum) the standard is that they enter their email once or twice, and their password twice.
The only company to lean away from this that I've noticed is Facebook, who have you enter your email twice and password once.
Which would you do if you were starting a project? I can understand that many Facebook users will be reusing their dictionary-word password everywhere, but I can see both pros and cons to only asking for a password once.
WWHND?
Here is my rational for making the switch. I want users to become engaged. The fact that they are registering means I did something right that motivated them to act. I require, like many others, to validate their email and account by clicking on a link that gets emailed to them. If they never get the link they never get fully registered. I am sure a large number of users would not follow up on this. They were motivated at the time to register but that motivation might not be strong enough to persuade them to troubleshoot their registration. This results in turning a motivated user into a disgruntled surfer.
Plus if the password was wrong they can always reset it with their validated and confirmed email