While it is no problem for the slashdot crowd, less tech-savvy users have huge problem with even the smallest change.
Here is one example:
I have a friend in his 50ties who just started to use computers and the internet. He barely known what a search engine is, and often has problems reading the small font of tool tips etc. He used IE8 and was used to type into the "Google Box" to search. Along comes the change to IE 9 and all of a sudden he has to use the URL bar to search. He has problems with that. This is not what he learned and how he expects things to work.
He also had problems when his mail client changed the Icon to write e-mails from "Mail" to "Compose".
A Hammer is a hammer is a hammer.
In the real world tools do not change how they are operated.
Even cars did not change their UI in the past 100 years. And the elements that did change, are often not used by everyone. How many people do you know who do not know how to set their clock correctly? Who do not use their GPS? VCRs are/were known hard to use, because each and every one has a different way to program a recording.
While *I* love new UIs and shiny things in general, there are lots of people out there who cannot abstract computers and are lost when small things change.