I love dropbox (use it daily, but only the free version). To be honest I think this decision will probably be looked on as a mistake. Personally, I'm moving to iCloud soon. The reason for this is that it will enable syncing of the notoriously closed Apps and music that come with Apple. The non-apple crowd will not see this benefit, but once Google or Facebook decide they want to be in the cloud storage game too, Drop…
There is a lot to like about Dropbox, but you really really can't just brush off the installed base of Apple. If anyone has their customers by the short and curlies Apple does.