Will I be penalized if my URLs all have the same priority?

Matt's answer:
CUTTS: All right, AndyPTG from Boston asks, “Will I be penalized for having every file in my XML Sitemap listed with the same priority? I get a warning about that, but the same time, you know, the priority field is optional.” Well, I definitely don’t think you’ll be penalized. If you give all of those files the same priority, then we’ll just try to sort out which ones we think are the most important on our own. So I definitely wouldn’t worry about, you know, having to list a priority for every single one. It’s not like we’re going to have some scoring penalty or anything like that. It’s totally fine and it’s totally optional. So, if you do have some information that you can use to put in a priority, that’s great. But it’s not required and it won’t get you in trouble if you do or don’t have it.
by Matt Cutts - Google's Head of Search Quality Team