As iOS 4 is being released for upgrading today (you'll need iTunes 9.2 to do so), a lot of new features will be introduced. Many are brand new, but some resemble features introduced with the iPad and iPhone OS 3.2, and are improved beyond that.
One of them is the Location Services Settings, especially with respect to privacy controls.
In iPad, a little NE pointing arrow appears in the top bar to alert you that the GPS is being accessed from an application, and that function is now in iOS 4 as well. [crarko adds: My mistake: it appears this wasn't in iPhone OS 3.2, and is new.]
What's new is the ability to toggle on or off the ability of apps to use Location Services on a per app basis, much like Notifications. If you look in Settings » General » Location Services, all the apps that make use of the GPS are listed, along with the NE arrow icon if they have used Location Services in the past 24 hours. There is also a toggle switch for each app, to enable/disable the services.
Note you will no longer be presented with the dialog box asking for permission to use your current location in apps, but will instead be warned by an app that you've turned off that it can't get current information. An app which is enabled will display the arrow icon.
[crarko adds: This is one of many subtle improvements in iOS 4. Besides the information available from Apple, check out this article for a quick overview of what's new.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20100621052550700