I certainly consider ebooks and PDF’s to be effective lead magnets. How? It just comes down to providing something that someone considers to be valuable.
We offer freebie whitepapers like Marketing Automation 101 or this report that compares our software platform to some well-known competitors and we have people downloading them literally every day.
As for “effective”, well, lots of these people go on to download more assets and/or book a demo with us. So yes, in our case, these assets are effective.