I just tried Tennis Round on the new iPad 2. It’s super fast and responsive (both the site and the device). The list of courts refreshes almost instantaneously when you drag the map. Tooltips pop up at the touch of a finger tip (imagine that!). Works much like an app, though it’s a website.
Looking for tennis players and sorting by skill level works fine, too. Though it comes with a funny behavior (it’s not an app after all) from clicking on the Invite Player link – you have to click twice before you can compose a tennis invite.