I started using the WP Pretty Link plugin for my external cryptic links.
Rather than linking directly to, for example, my picasa photo albums I link to mysite.com/picasa/album5
and WP Pretty Links redirects it to the real url.
This way I can always update my Pretty Links without changing my website links.
Search engines won't collect my sensitive urls, I reduce 404s, and I can add a layer of privacy, in case I need users to first log-in.