I highly doubt Apple would use a removable battery for several reasons.
First, Apple loves to use new materials. They redefined what you could do with plastics with their color iMacs, made innovations in manufacturing aluminum, and even created a new rubber like material for the non slip grip on the bottom of the new iMacs. Batteries doors almost always create design limitations. Just look at the aluminum macbook with a battery door. They went out of their way to design that door. Second, apple loves internal batteries because they allow for longer battery usage. Apple, as we all know, is a stickler when it comes to battery life. New features like an led flash or multitasking would likely suck up battery. Apple, if anything, should be trying to increase battery life. Third, I don't see much use in a removable battery. I have never wanted to swap a battery with my phone, or even my laptop for that matter. I don't really see the point; it's not like tons of people go and buy extra batteries for their phones anyway. I only think this would be a reality if Apple released a Pixi like competitor in April. I doubt Apple would break tradition and announce a new iPhone 3gs HD early. This probably means that a phone will be announced at the developers conference if they announce multiple screen resolutions. This will probably be done in order to keep their stocks under control. Imagine if apple had announced months ago the created software for a tablet but said that they had no intentions on creating a tablet device. Anyway, that is my opinion on the current situation.