Excel files, and only excel files are very slow to cloud sync. LANsinc is fast but the sync indicator on the dropbox icon stays on for a long time. I tested by saving a very small excel file, 10kB, takes 10 sec. A similar size file of any other type, including Word, will cloud sync in 1 or 2 seconds. I have no limit on dropbox speed and my upload speed is 6Mb/s.