Comment most apps are likely using it for analytics (Score 1) 194
The UDID is really useful for collecting analytics, such as with Flurry Analytics.
You can really easily get nice graphs and charts on how users in aggregate are using your app, or drill down to any particular (anyonymous) user based on the UDID.
For these analytics to be useful, you need to specify some type of unique identifier for the device. A UDID makes perfect sense, and there really isn't any standard or easy way to map the UDID to any particular user anyway, so it's hard to see what all the fuss is about. Regardless, the app should let the user know the UDID is being logged, and allow them the option to turn the logging off.