Scott

It's more like a case to case situation.

Typically you should shy away from companies who are building a brand reputation - i would never include geico , farmville,facebook , google in a domain.

On the other hand i consider it totally safe if you use names of companies whose business model is typical direct marketing ROI based advertising - examples include of what you see on clickbank & cpa networks.

So if you are referring to Amish shah's Magic Bullet - i would go ahead and do it - exception being that if their affiliate program specifically forbids it - in that case i would still go ahead and divert traffic to another offer.