I started EmailItIn[1] to allow people to email files to Google Drive, then added DropBox and SkyDrive/OneDrive support. Premium accounts bring in about $200/m right now, and it's steadily rising.
Support is low - though it took a while to build the initial technology. I get a lot of traction from realtors and lawyers. I've tried paid advertising but the conversions are too low to make it worth it.
Initial goal was "vacation money", and it's currently on track to hit that level next year.
What do you charge for premium accounts? I can't find pricing on your site.
I've had a similar service, http://dbinbox.com/, slowly growing with entirely free plans for the last ~year and a half up to ~25k users and am about to add premium plans.
25k users is amazing. With a premium plan you should be able to convert that into excellent revenue. I suspect getting on CNet, Lifehacker and PCWorld helped a lot there - mind sharing how you got published in those places?
The site is a bit lacking in documentation (typical side project issue). It's $3/m or $30/year. I get a good mix of both types of subscriptions. I figure the price is low enough that it's not a barrier to entry for the majority of people. I also need to document better what premium accounts get you (ability to upload to different folders, etc).
Without paid advertising, how do you advertise the service? I've created a micro-service like this in the past, and where I really fell short was getting the right people on the site. AdWord conversions were also too low in my case.
I worked hard to get onto the front page of google for "email to google drive", and I have a few links from other places that drive a bit of traffic.
I experimented with adwords and stumbleupon but nothing caused enough conversions to be worth it. Every now and then I turn adwords back on to play with keywords a bit, but it's just not worth it at the low price point.
I forgot to add - my next project is likely to be re-writing DVDSpanner (an application that automatically distributes and writes files across multiple disks) to support the latest OSX versions. I will be making that a paid app. I was inspired by the recent story about VirtualHostX.
Support is low - though it took a while to build the initial technology. I get a lot of traction from realtors and lawyers. I've tried paid advertising but the conversions are too low to make it worth it.
Initial goal was "vacation money", and it's currently on track to hit that level next year.
1: https://emailitin.com/