What exactly makes them incomparable? I think it is fairly apt. They were both the "one more thing", both were Apple versions of existing technologies that some people are claiming will succeed mostly cause they are Apple versions, they are really power user features that lack mass adoption currently, both face social mores that make their use somewhat awkward and so on. I think all signs point to Facetime the sequel. A damn good product that is used once or twice to test, a lot by a couple of people, and is mostly inconsequential.
For one thing, FaceTime is a multi-party tool which falls victim to the network effect. The first people to get an iPhone 4 had few people they could FaceTime with, so it wasn't very useful to them.
Siri, on the other hand, doesn't depend on anyone else having anything in particular. Siri would be just as useful if you were the only person on the planet able to use it. I think that will make a huge difference in adoption.
What?! No, certainly not. When FaceTime gets adaption you will not know whether Siri will also be able to get adaption. The reverse is also true. They are completely different features.
