How many designs on iOS?
In the meantime I have learned about users holding thousands of designs in StitchBuddy HD / View, unfortunately pushing these apps over their limits: The flat gallery can't keep track of all the preview images, literally running in cycles, the synching can't complete in time, and the apps might stall or even crash. These issues are high on my priority list, and after releasing the iOS 7 versions my next goal is to improve StitchBuddy with a more robust and powerful gallery and synching process, so you can save and manage more designs on your iOS device.
But how to handle the current situation? I recommend to put subfolders into StitchBuddy's folder on Dropbox and put the majority of files into these folders: StitchBuddy won't synch them, keeping its number of files at a manageable level, and you can use the Dropbox app on your iPad / iPhone to move working files to and from the application folder. For sure only a bypass, but at least a possibility to have all your designs at reach when being mobile, and still keeping StitchBuddy responsive.