In reply to captain paranoia:
No, Apple weren't (and aren't) slowing phones all the time to give a worse user experience with the objective of forcing an upgrade as was claimed and denied. As the phone batteries aged, there was a problem that, at peak processor load, they would suddenly shut down because the battery could no-longer deliver the required power.
Apple's response was to introduce a change to the power management software so that as the battery deteriorated it would limit the maximum processor load rather than have these crashes - most of the time the processor is nowhere near max so there is no effect. If you replace the battery then you are back to new phone performance. Wicked price-gouging Apple will replace an iPhone 6 battery for £25.
I absolutely agree that power management v performance should be a user - managed option and transparency is never a bad thing. If Apple had announced a new option (rather than a hidden change) to avoid these crashes and been more transparent they would have avoided a lot of negative publicity but anybody who chose to keep having sudden crashes rather than replace the battery or accept an occasional throttle back would have to be a bit of in idiot IMO.