Quilts and bags with no insulation on the bottom are good if you sleep on you back and don't move at night. But if you rollover or sleep on your side they can have cold spots and let cold air in. Also no hood makes them feel colder than a bag with one
Well, ideally a quilt should be wide enough that that you can roll over without loosing all your heat. If your quilt is too narrow, that certainly can happen, and it does suck. All the more reason to get a nice wide one, you're already loosing weight swapping from a sleeping bag, so get a really wide one.
As far as Sport10y's question, the end with snaps forms a box for your feet, you sleep on top of your pad (some people include a liner for comfort), and you cinch the top around your neck. In very cold weather, a quilt should be supplemented with a beanie or a balaclava.