Andy Sernovitz, Word-of-Mouth Marketing specialist, had a good post about trade magazines.
Two sentences that I found to be the most valuable from his post are:
"Trade mags are your free ticket to diverse knowledge about all sorts of markets."
"I know a little bit about a LOT of businesses. "
I agree with Andy that it is a good idea to subscribe to trade magazines or at least set up some RSS feeds for various trade magazines.
It’s also a good idea to look at trade magazines in a variety of industries. Articles and ads from other industries can provide ideas and spark creativity.
In addition, they can make you a more well-rounded conversationalist. Most are free as well.