Simple and Usable

is an excellent book by Giles Colborne (isbn 0-321-70354-5). As usual I'm going to quote from a few pages:
If you ask people they'll say everything is important and anything is feasible.
We tend to keep things, even when they're broken.
Your first design may seem like a solution, but it's usually just an early definition of the problem you are trying to solve. [Luke Wroblewski]
Broken gets fixed. Shoddy lasts forever. [Jack Moffett]
Feature lists sell so as long customers don't get a chance to use the product.
Mainstreamers want "good enough quickly;" experts want "perfect in as long as it takes."
People prefer to be pilots, not passengers.
"Seven plus or minus two." Many psychologists now believe short-term memory may be rather smaller - perhaps just four items.
Simple organization is about what feels good as you're using the software, not what looks logical in a plan.
Designing simple user experiences often turns out not to be about "How can I make this simple?" but rather "Where should I move the complexity?"
The secret to creating a simple user experience is to shift complexity into the right place, so that each moment feels simple.
Don't try to fill your user's mind with your design.