Ask HN: Thriving side-project, thousands of users. Now what?

This 'Proposition HN' thing got me thinking... I have a side-project with tens of thousands of users and I have no idea what to do with it. It's an interesting situation. I launched the project almost 2 years ago, and I kind of just expected it to die. But amazingly enough, it's growing - organically, all by itself, with no advertisement, promotion, or effort of any kind of my part. The project is www.boxify.me - a simple file-sharing utility for groups. Apparently people find it useful, because nearly 100,000 files have been uploaded, with hundreds more added daily. I've had people outright offer me money for a premium version (that doesn't exist). It has been featured on Lifehacker, GigaOM, AddictiveTips, etc - none of which I reached out to. That says something. All of that and I basically haven't touched the codebase since launch (aside from slight styling and recently upgrading to Rails 3), nor have I attempted to monetize. My dilemma is that this is not a project I'm particularly interested in at the moment. And with a full time startup job, I don't have much time to invest in it. The hosting bills are costing me a pretty penny, but I can't just kill the project with so many people using it. I've pondered selling, but there's huge potential and I'm not sure I want to pass it up. Maybe a co-founder or partnership is a good solution. Any ideas?