Subscription option to remove ads and provide personalised user space
For a small fee of maybe $25 / year a user can login to remove ads and get access to a personalised space with "my locations" for bookmarking locations and "my uploads" for hosting KML, GPX, etc. files on the site directly that can be private or shared.
If I was to offer a paid option I think I'd like to provide a bit more value for $10 / $10 a year. Perhaps a "my places" for bookmarking locations and "my uploads" for adding kml / gpx files, with the option of making the files shareable. I think I'll add that as a new suggestion to see how much interest there is.