I tried YNAB for the trial period and did not buy it in the end. I still use Mint (and spreadsheets and google calendar) to this day, although it has its own set of problems. They are two different tools with different advantages and disadvantages. I didn't really feel like I needed a budgeting tool as much as I needed a tracking and reporting tool, so I stayed with Mint and passed on YNAB. The application itself is nice, seems polished and friendly and all that, it just didn't do what I was looking for (or maybe, I was shopping for the wrong product).
In the end, I think the main problem for me was that we're in debt payoff mode, so YNAB would always show me in the red and be unnecessarily complicated to use unless I could afford to keep $10,000 (not an exaggeration, my monthly outflow has varied between $6,000 and $9,900 in 2013) in my checking account at all times. If I have $10k in the checking account, its going towards paying off the truck or the student loan RIGHT NOW. So given the last conversation I had about these two tools, you can consider me living paycheck to paycheck in that sense, which YNAB does not want you to do.
After we hit 0 debt? Yeah, I would give it another shot. That's years away right now though.