The only marketing partnerships I've had have been between companies I owned; I'm cautious about tying my business reputation to someone else's. That's the main risk, I believe, of doing a cross-promotional deal. Whatever trouble your partner gets into will leave a stench on you. That said, I don't see anything inherently wrong with the practice. In fact, one of my new companies is negotiating several cross-promotional deals right now, though only with companies I know well.
In that sense, a marketing partnership is like any other partnership. The first rule is: Know your partner. If you haven't done business with the company, do research. What is its reputation for honesty and integrity? What experiences have other companies had working with it? How does the company treat its employees, customers, and suppliers? What are its motives for doing the deal?
Let's assume that the other company's reputation checks out. You should also investigate whether your presumptive partner has similar deals with your competitors. If so, it might be to your advantage not to do a cross-promotion and instead use your independence to set yourself apart. Or you could see if the other party would be open to offering you an exclusive arrangement.
If you do decide to move forward with the deal, be sure to take into account the possible results, good and bad. Do you have an escape clause in case the partnership winds up creating more problems than it's worth? Alternatively, can you extend the arrangement if it works as well as, or better than, you hope it will?
The chances for success in doing cross-promotions depend on how well prepared you are before you sign the deal. As with most things in business and life, you need to do your homework.