[astrec]

This is more along the lines of what I was thinking.

I'd normally call, get as close to the decision maker as is possible (not always easy in big companies), tell them you're sorry that you weren't up to snuff, then LISTEN.

It's amazing what comes out of these conversations: Your product might be slow, missing a feature, their general counsel might have had reservations your startup, your account management might suck, the decision maker might play golf with the CEO of the other company etc. etc.

Your guess that your users are choosing our competitors because they have better features and more customization options is correct in only one of these cases. You're doing a startup: You don't have time to fix problems your customers don't have. So ask.