FWIW, in this use-case the limit is the wifi or more likey your internet connection speed. You don't really need blazing disk read/write speeds for your "Dropbox clone" - if you can read and write data as fast as your adsl connection goes - anything more is "wasted". As a general purpose file server though - yeah, a 'Pi isn't going to stream multiple HD videos to all 4 bedrooms on your home network.

Both my wifi and internet connection speed are well over the 2megabytes/s I'm getting on my pi, which really is the only downside I have found with my pi.

When I setup a file-server for myself, I set it up on the local network I use most, so the Internet speed is relevant, but not that much.