Ubuntu works just fine for two kind of users:

1.) Grandmothers and the like who just want to read their mail and check the news.

2.) People like me who can and will use 4 + 2 + 1 + 0,5 hours to customize it over the course of 6-12 months to have an almost perfect working environment instead of living with a slower OS without virtual desktops.

The only thing I can think of that needs tinkering is some online banks that require applets to work, but then again even Windows doesn't come with Java preinstalled.