Good point about it being a double-edged sword, but I think strategically it's better to rely on an existing service (allow use of multiple services to diversif

Good point about it being a double-edged sword, but I think strategically it's better to rely on an existing service (allow use of multiple services to diversify the risk). If the services disappear, yes, you're a bit SOL but I'd deal with that when it happens. Better to get something working first and get customers and not worry about running a sync service. This is all under the assumption that your app doesn't require something beyond basic file sync, of course.