Launch Center is a new app for the iPhone that takes advantage of URL schemes. You may have seen this term flying around a bit recently, so let me just explain it for clarification. Essentially, a URL scheme allows you to 'link' to something. An app, for instance. Or 'link' to a particular preference pane in Settings (although Apple is removing this particular functionality in iOS 5.1, supposedly). By following these special URLs it will redirect you to where you want to go. Launch Center presents you with a pretty list of your custom 'links' and allows you to tap on any one to bring you to whatever you have it set to bring you to.
Follow? I know, it's a little complicated. Which is why, instead of simply sending you to the app itself, the link above will send you to a nice overview of the app, along with some ideas for practical use of the app. It'll give you a better idea of what the app really is and how it works, as well as how it can help you on a day to day basis.
Personally, I don't really see a use for this in my use of the iPhone. I use Dialvetica for the quick calling feature, and don't see how I would really benefit from most of the other features, but some people as of late really swear by it. Maybe you will too. I could certainly see how it would be a nice app to have around.
UPDATE: I have since purchased and started toying around with this app. As it turns out, it does seem to be rather useful. It's like having a bunch of apps all in one with super fast access to them all. I also like the Tweet and Flashlight feature. I suggest downloading the app and trying it. You'll find it's actually more useful than it may first appear. It now resides on my main homescreen.