If I've learned one thing in 15 years of being a business owner is that trading your services for exposure rarely pays off.  I have never gained the promised exposure by giving away my services in trade.  

Remember you are not only giving your time and talent for the actual event or project but also lead time and post-production time.  You'll have logistic emails and calls to make with deadlines to meet.  Again, if you are trading services for exposure you better make sure that the entire "deal" is ironed out and in a contractual form as a handshake isn't good enough. 

Keep this in mind when being asked to donate items for charity auctions, fundraisers, etc.  Most often those who win these actions or fundraisers aren't your ideal clients or fail to redeem the offer.

Okay, I know I sound like Debbie-Downer so let me follow up with this... if you feel called to donate your time, talent or products, do it out of the goodness of your heart with no expectation for exposure.  For example years ago, I donated my time to Help Portrait and felt far more fulfilled creating and providing those who attended the event with images than giving away a gift certificate to never be used.

What about collaborations with other industry people? 

I think collaborations are a fabulous way to network and meet other like minded creatives and business owners.  Again, make sure that all of the details are ironed out as to who is expected to provide what for the project and that realistic deadlines are created for everyone.