A comment to the last post wondered if drug companies ever do active intelligence against each other (as opposed to the passive kinds I mentioned). Active means would be rooting through dumpsters and the like, and the answer is - almost invariably - no.
That sort of thing is more trouble than it's worth, because it's easy to find out what's public knowledge at a given time and what isn't. If you dig around for nonpublic information, it doesn't do you much good unless you act on it. And if you act on it, you've admitted having something that you shouldn't, and you're faced with having to explain your psychic powers.
The same problem occurs in military and governmental intelligence gathering, on a rather larger scale. But there the theater the intelligence is gathered in is the same one where any repercussions will occur (in diplomatic relations or on the battlefield). In business, the retaliation will come through the courts, which is a completely different problem, and generally one you don't want.
If someone talks more than they should during a meeting, well, that's their problem. The listeners always have the defense that they didn't think that this was truly proprietary information, because if it was, the speaker wouldn't have let it out, right? But that said, I can't think of any major slip-ups of this kind - perhaps some of my readers know of a few.
The only active intelligence gathering I've heard was in a story that broke a few years ago. It seems that one or more large European pharma companies were trying to figure out what some of the patent-ignoring generic drug firms in Cyprus were up to, and hired some folks to sneak into some offices to see if their drugs were being pirated. A couple of people got caught in a break-in. I haven't seen a follow-up in some time, so I don't know what eventually happened. There was an interesting article in Fortune in 1998 or 1999 on the case, but it isn't online.