Then why validate at all? Just send the user an email with an activation link. If it doesn't work and they're still logged into the site (with a limited account), then let them change their email address.

If you want your site to have a "login as guest" type feature that's one thing, but if an email address doesn't have an @ it will never work and it would be misleading to encourage people to check their email for a validation link.

People sometimes misread labels and enter their name on the line for their address. This would stop that.

Yeah exactly. It's more to catch wrong stuff entered in wrong field.

I had people write www.hotmail.com in the email field in the past.

In my experience, the most common problem with user entered email addresses is that they've mistakenly used a comma where they should have used a period.