I first learned of Zeal several months ago...and i really like it. But, i forget about havign zeal installed and available, that my reflex is to instinctively reach for duck duck go, or stack overflow, or somesuch search engine, etc. So, i just gotta build up the habit. :-)
I understand completely. I even wrote an offline documentation browser [0] for Linux similar to Dash, and I reflexively search online too. It's a hard habit to break, but I think it's a UI/UX issue.