Every entreprenuer should read Chapter 8 of The Art of the Start by Guy Kawasaki. I think he does a nice job of capturing the benefits of "partnering". He also captures what I consider key in engaging legal counsel to assist you in realizing your business goals. Here are two paragraphs starting on page 158:
If there's one way to ensure that a partnership won't go through, it's asking for legal advice too early. If you do this, you'll learn that the number of reasons not to do a deal always exceeds that number of reasons to do it. The point is to agree on business terms before you bring in the lawyers. Then find a lawyer who genuinely wants to do deals, not prevent them, and set the right legal framework.
Many lawyers view their role as the "adult supervision" that will prevent stupid deals from taking place. However, their bias is often that a deal is bad until proven good. Avoid this kind of lawyer. Instead, find one who views his role as a problem solver and service function for you, the customer.

