Touch here; See instructions below.
When two simultaneous touches are registered, the orange bar will turn green.
For me, about 1 in 3 touches with the second finger has serious lag or is not recognized at all until I move my fingers.
Try it a few times!
This bug is a serious show stopper for HTML5 Gaming: you can't press two buttons at the same time. For a real example, try playing Biolab Disaster, you can't jump (reliably) when running.
This bug seems to exist only on the (my?) iPad (iOS 4.2.1). It works perfectly on my iPhone 3GS (iOS 4.1).
Update: Upgraded my iPhone to iOS 4.2.1 and now have the same problem. This seems to be an issue with iOS 4.2.1. At least it's not a hardware bug.
Update (2011-10-13): Still not fixed in iOS5. Apple, you really suck at this whole developer relations thing, but you couldn't care less, right?
Update (2012-05-16): Still not fixed in iOS5.1.1.
Update (2012-06-13): Still not fixed in iOS6.0
Update (2012-07-16): Fixed in iOS6 Beta 3