UIProgressHUD – The Undocumented Alert Type
I really like this type of alert view to inform a user that some background processing is going on but it’s a real shame that it’s an undocumented and private class, meaning therefore you run the risk of your app being rejected by Apple if used.
What’s odd however is that I've seen many approved applications use this particular alert view so i guess it’s not 100% guaranteed of breaking Apple’s policy. I'm personally very keen on implementing this into my next iPhone application, it simply looks the part. Implementing UIProgressHUD Using the undocumented approach in your project is nicely explained here http://tmdvs.me/post/uikit-alert-types and i've tested it against the current iPhone OS version 3.1.2 and it still works well, however if we wish to avoid all possible risk of rejection by Apple, i found some code that someone has took time to develop that does a good job of replicating the undocumented alert, called MBProgressHUD
http://www.bukovinski.com/2009/04/08/mbprogresshud-for-iphone/
I’m personally going to try the undocumented method first and see if Apple accept it with my next application submission.