It's extremely useful to - Have a virtually unlimited undo history, and - Have it persisted even after exiting VIM, and - Better, even have it synchronized across all your working machines using Dropbox.

Sometime this error occurs that says:

"Unable to monitor file system. Please run: echo 100000 | sudo tee /proc/sys/fs/inotify/max_user_watches and restart Dropbox to correct the problem.