Will you have a Linux client? (I'm sure that's the least favorite question new services like this get.)
I ripped Dropbox out by the roots on all of my systems some time back because of the contempt they display for their users. New, more privacy- and security-conscious services are nice (as are ones that don't break their users' machines and then go weaselly when caught). But I really want the option to use my own infrastructure for apps that want to store data somewhere remote.
Especially for file-based services, the only argument for Dropbox is "because they're big and probably already installed"[2]. I'd deeply appreciate it if these sorts of apps would add a preference-pane for scp, at least. I have no idea if the crusty-folks-like-me market is big enough to constitute a noticeable bump in app store sales or not, but I promise, given two competing apps, I'll forgive a lot of other warts in and pay more for the one that lets me own my own data.
[1] I know cloud is king, but there are a lot of us out here that want to own our own data, rather than having the cloud-overlords rent it back to us. The Omnigroup's apps are great examples of this - you can use their sync servers, but you can also (and I do) run your own WebDAV server for it. Works great, and I have paid the Omnigroup substantially more than any other single mobile app vendor for their apps.
[2] Synchronization is difficult enough in some contexts that I completely get writing something more complicated there, but then we're not talking about Dropbox or their competitors anymore.