Add a function to save your entire ToDo list as a single file (csv format, for example) to allow easy archiving and exporting.
I second this suggestion wholeheartedly. I'm far from leaving Todo (Todo Cloud), but I certainly feel better performing my own regular backups, if information is particularly meaningful to me. A simple plain text file would do (e.g. comma, semicolon, tab delimited). XML as well. In fact, just to have all of the tasks in a list for copy & paste would be good enough.
Let me echo what Lech said and add that as a new user, switching from another task management system, I really want an easy way to import a lot of tasks.
If you could upload a file that used even the same syntax as the email #tags, etc. it would make a huge difference.
And, of course, it is bad Internet manners not to allow people to export their own data whenever they want.