I don't know about all Marriotts, but the DFW North Courtyard said they would print your boarding passes for you with no charge. When I asked at the front desk, they thought that while most any Marriott would do this, they didn't think a lot of them would do it for free.

BTW, I stayed at the Downtown Dallas Hyatt last weekend, and they had signs posted everywhere about their print services for boarding passes. For only $10 they would print out your boarding passes.