3D Level is handy water level -- taken to the third dimension! A water level like you've never seen before. Check if your wall is 90 degrees off level, then if your table is level, all without (re)calibration. Maybe you can find other uses for it as well, like err, using it to check if you're too drunk to drive a car! ;)
The app comes with two sounds indicating the the iPhone or iPod touch is now level and when it's not level anymore.
The app works when it's placed in landscape or portrait. If you rotate the device from landscape or portrait, 3D Level can't get accurate measurements. Additionally, please tilt your iPhone/iPod touch just a little in one of the 2 dimensions you aren't measuring if you think the surface should be level and 3D Level isn't showing it.
3D Level has been finetuned for the iPod touch 1st and 2nd gen and iPhone 3G so that it doesn't need calibration. It is currently UNTESTED on iPhone 1st gen and iPhone 3GS and without correct algorithms for these devices, may display incorrect results.