I would like to let you know that I'm writing some lines (and hope to post them here soon) about MS Dynamics CRM 4.0 and Marketing Newsletters.
As we are testing and developing our CRM 4.0 we are spending nearly 80% of our time trying to understand and overcome some limitations regarding this marketing process. We even developed a specific workflow to send newsletters from Queues and another one just to handle errors (Mail Delivery Failed, Undeliverable...). These workarounds are not perfect but they are very useful for us. I will also tell you how the unsubscribe works (dynamic, hardcoded...).
But you'll have to wait a couple of days because I'll be on holidays during next week.