Speculate all you want about what users expect, what they want, what they care about. There’s no substitute for actually running experiments to find out. Those who haven’t already been following Jensen Harris really ought to be, because he talks about user interface design in a highly practical way. Consider this entry on deciding how the ribbon should behave:

These rules came directly out of watching people use the product in the labs over the last few years. Other rules we thought would be important (such as always collapsing from right to left) turned out to not matter at all.

Or this one on the special rule for lingering:

What we found was that an extremely common scenario involved people using an object, clicking away from it to make the selection handles go away (to get a better look at it) and then clicking right back on the object to continue formatting it.

Notice that prior to discovering and then implementing the “lingering” rule, users who used Contextual Tabs were frequently confused. But once the rule was created, the usability results are solid.