Try out Gliffy.com
Check out Gliffy's blog at http://www.gliffy.com/blog/. One of their latest posts is on a new plugin to Confluence, an Enterprise Wiki (http://www.gliffy.com/blog/?p=41), so it looks like they are very busy over there. Hats off to Chris and Clint!
Now to tie this into backup - this is another opportunity for backup of online content. I have some documents stored up on Gliffy I would not be happy with if they "went away". I really ought to have a backup but currently there's not much I can do to make that happen. I guess I could go through and save a .PNG of each document each time I make an update. Not practical.
Gliffy doesn't have an API (that I am aware of) to suck a copy of your files out. Maybe a "Save as Visio document" feature would facilitate the capability to provide a backup.
Well, needless to say we are going to look into adding support for backup of your Gliffy documents to BlogBackupOnline.com. We will let you know how that works out.