After installing, you'll be prompted to create a free account (which you can also do at tektrak.com) with your email address and your phone number. A confirmation splash screen suggests you try the service out at TekTrak.com, and after continuing, you're shown which features are active.
TekTrak's location tracking takes advantage of iOS's new background location service, which should detect when your phone changes locations. This uses less battery life than monitoring an always-on GPS signal would, and will also keep running in the background after you restart your phone. Unlike Find My iPhone, which checks in with your phone when you look for it, TekTrak transmits its location changes so that you can review them on the website. If your battery dies, you'll still know where the phone was last seen online, and everywhere it went before that.
Be careful, though. If you decide to use the website to find out whether the app is working, you'll use up your free uses. I checked the location, then checked it again a little later to make sure the updates were being sent, and I had zero uses left. Since TekTrak offers three features (locate phone, remote ring and location history), they really should offer users five free uses. The first three will get used up just learning how it works.
TekTrak says you'll get a free use for each friend you refer to the app, so refer a lot of friends if you're the sort of person that wants to check whether your apps are working.
Also keep in mind that while TekTrak offers a location history that MobileMe does not, the app has a couple drawbacks. Because of limits on what apps can do in iOS, TekTrak can't override the ringer volume or silent mode on your phone, and it can't remotely wipe the data from your phone if you left it in a place you're not likely to get it back from, such as the back of a cab.
iPhone 3GS users who don't want to pay a MobileMe subscription should check this out, and at just $4.99, TekTrak Pro's location history is an easy way to not only find your iPhone but also see where it's been.
Watch a demo video of the app in action, or grab TekTrak free on the iTunes app store.