I urge people to think twice before publicizing their UDIDs. Many apps have very serious shortcomings in the way they deal with UDIDs, which means that an attacker armed with your UDID could potentially access accounts and personal information.

See here for some recent examples, looking just at a single industry (social gaming networks):

http://corte.si/posts/security/udid-must-die/index.html

I can tell you with absolute confidence that this is just the tip of the iceberg.

Sorry to report some bad news, but I just received an application error. If you'd like full details (platform, browser, etc) ask and I'll send you my details!

One question: When a friend send me an app do I have option to say 'NO' before app installs itself?

Uh, at first I misread this as UDDIDirectory, and was very glad to realize that was a mistake.