Ask HN: Free online eBook + sell PDF/ePUB, or just sell PDF/ePUB eBook?

If you were writing a technology centric eBook, would you publish it free online and sell a digital eBook (PDF/ePUB/etc.) and Print on Demand version, or just have it for sell with a free sample chapter like most traditional publishers? I'm noticing many online eBooks that are available fully free online but with for pay extras, http://railstutorial.org being a good example. The free content would obviously be a great way for people to discover your writing, but also lowers the likelihood of them paying. Then again, a for-pay eBook that no one knows of won't get sold either. Most of all, there's no reason we need to stick with only the most traditional sales methods with eBooks.

What's your feelings about each method, and which would you choose? I've almost decided what I want to do, but would be interested to see the general thoughts on both models.