HTC Nexus One

The short answer is that it's more like the iPhone.

The kind of touch sensor the iPhone has is called capacitive. It responds the electrical properties of your finger (not heat.) It's generally considered the better kind. Most people find it more reliable. It responds to the lightest touch; it requires no actual pressure.

The other kind is called resistive. It responds only to actual pressure. They can be tricky to get used to, especially if you're used to capacitive, although once you get used to applying the right amount of pressure, they do become easier to use than at first.

Both types have good and bad implementations. I've used some very good resistive touch screens that felt almost like capacitive. I've also used terrible capacitive touch screens that were a nightmare to use.

But in general, most capacitive touch screens are quite good, while resistive touch screens are not as reliable. Most people who have tried both prefer a good capacitive touch screen.