Yes, and ideally we should have the ability to do this based on custom field we add to the sign up form.

This would be super useful.  Manually adding members to groups one at a time is not reasonable when you have hundreds of members.  Having to add members one at a time means that we essentially can't efficiently use groups for most of our club's purposes.  If dynamic groups are more complexe for you to set up, at least giving us the ability to manually filter on custom fields to add a batch of people to a group would be critical in my opinion.