That made me thing though... can you trust your users not to expose their private URL addresses? Aren't you trusting it to them, and if you have a user without internet experience signing up, what happens if he submits his private URL to google and makes it public? Doesn't that create a security hole?
Putting any sensitive information into a url is bound to be exploited sooner or later. Liberally, you can hold the info in urls for the duration of user session but anything beyond that is totally unwise. For the reasons you already mentioned.
Other possibilities for unintentional exposing of your personal ulr include: - Users who have google/alexa/amazon/etc. toolbars installed on their browsers, they browse to their personal page, or maybe bookmark it, and alexa/google immediately realize that it is not indexed so they start crawling it.
- Other phenomenons like Google Desktop Search crawls and caches all user bookmarks.
You should not use http GET method to perform unrelated operations. If you want to offer a delete option to your users, use http POST method. For authentication purposes, i absolutely recommend using HTTPS with POST method.