I've read a few blogs where the authors complain that they give away huge numbers of articles and less than 1% of the visitors donate.
I think it depends on what you're doing. With the music industry, you can give away your music and then get the fans to pay for a show and merchandise. In that regard, the path is pretty clear. And yet, even the music industry complains about losing tons of money to freeloaders. It's about the time/money ratio. Time and money get's spent on marketing the artist, recording the music and distributing it and the consumer steals it on the other end. That's not giving away free content, that's having it taken away
Otherwise though, it's really a marketing ploy. I happen to like Drake and he's getting pretty big. No doubt business is general is changing and this is one of the directions it's going. Reciprocation is definitely a powerful tool, although it's usually far more subtle.
Here's a couple examples I would bank on:
Doing a free speech and offering books or coaching services = +++.
Selling a food product and offering free samples = +++.
If I take five hours to prepare a free speech, it's not a big deal if it doesn't pan out.
If I take 300 hours to write blog articles and no one pays attention/donates, then I'll probably do some crying and kick myself in the ass for my crazy business model.