I shot some video of a preview build for Harbor Master back at WWDC, and I'll upload that to our Facebook page later, but I also shot a quick video of Harbor Master's gameplay (on the next page). If you play Flight Control -- and those who do find it hard to put down -- you will absolutely love Harbor Master (iTunes link). The mechanism for control is the same: use your finger to draw a path to direct vehicles to their destination.
In this case you are controlling boats in a harbor. However, instead of merely docking them, you must juggle unloading their cargo (automated, but larger boats take longer) and sending them on their merry way. This pleasant twist on Flight Control's mechanics allows players of Harbor Master to steer clear of boredom.
Later levels add further twists, literally. One of the developers, Natalia, demonstrated a tiny hurricane, which will spin your boat around no matter what intended path you draw. Harbor Master also includes the requisite leaderboard, so if you like the high scores, you're covered (although you'll need to provide an email address and username).
The folks behind Harbor Master, Imangi Studios, have partnered with some other iPhone developers to provide some in-app promotion for each other in a service called App Treasures. Imagni also demoed another clever app, PhotoMarkr, at WWDC. It quickly and easily adds watermarks to photos on your iPhone. Check it out on the App Store here.
Update: fixed the Harbor Master link.