I'm far from a tech geek, I'm a science nerd, but not computer science.
We've all got the iPad here, it's a proprietary piece of hardware that people are generally unable to modify except for jailbreaking.
So if we all have the same hardware, and the same software, why are some users having a poor experience with the upgrade, and others (like myself) are having no problems at all? We see things like this a lot in the PC world, due to many different kinds of hardware and software being used, but that isn't the case here.
The only real issues I can understand is people having network issues, because we all have different routers with different settings, so problems could arise there between an individual's setup and the new 4.2.1.
Please explain to me in technical terms why someone using the same hardware and software (4.2.1) could experience a problem like excessive battery drain or slow performance?