Email verification is one of the first steps to preventing spam: it prevents people from using fake email addresses to access your site and then post spam. The email verification is designed to make sure that the people that sign up have valid addresses that belong to them. Therefore, we recommend that you keep that step enabled.
You could contact the people with unverified email addresses. Just filter to those users in the Manage Members control panel, select all of them, and then choose "Email Member(s)" from the action menu at the bottom, reminding them that they still need to verify their address. Give them a link to your site, and have them click on the "Resend Verification Email" link that appears at the top of the page when they sign in.
I suspect that the verification email is probably getting stuck in their spam filter, so you may want to mention that, as well: that they should check their spam filter for the verification email if they don't see it in their mail box shortly after they've requested it.
Hope that helps!