Short answer, I stick with what I know and am comfortable with.
Long answer however, I'm a creature of habit and old school so I don't like a huge shift in change of the software. But then, I spend a lot of time getting to know the ins and outs of the OS and making it exactly how I like after which is gets used heavily so I don't want to spend the time and effort in learning a new OS just for the sake of it. If something works well for you and meets all your needs, why bother going through all the effort of having to learn a new UI from scratch?
Changes in hardware are just fine, I switched recently from a pure keyboard to touch screen + keyboard where the symbols and other alt/shift/caps characters are slightly different. For the first few weeks, I was continually pressing the wrong key because I was used to old keyboard but this will change in time.
In contrast, the shift from say Windows Mobile 6.x to Windows Phone 7 was too much for me as I was completely lost. Hell, even the switch from BlackBerry OS5 to BB OS6 got me mad with all the subtle eye candy tweaks that changed everything
A quick straw poll around everyone here (about 15 people) shows an expected result: the young whipper snappers like to try different handsets and software and don't mind change as long as it has <insert favourite inane social media feature here>. The old timers generally do not like change and are more interested in how useful the handware/software is for them rather than trying out the latest cool new feature. Universally, very few are prepared to mess around with app stores as the general concensus is that their moby should do everything they want "out of the box".
iPhone is the OS virtually everyone would change to if forced due to ease of use and the lower learning curve. Android second but more for the curiosity value now that it's overtaken Apple.