Shop Talk: Tips for Confirming Email Sign-Ups

For the majority of folks (read: everyone who is NOT a spammer), I recommend the latter. Don't make the user confirm. If you do, you'll lose more than 40 percent to 60 percent of your sign-ups on average, sometimes more 
depending on your category and/or your target demographics.

It's important to note that there are some email service providers that insist you get verification. Before you sign up with an ESP, figure out what its policies are and how said policies impact deliverability. Also, find out whether it's an "all clients" policy or a "specific clients only" policy. Many ESPs recommend the verification process but don't insist on it.