I have been reading Emotional Design by Dr. Don Norman, a professor of cognitive psychology and well respected figure in usability.  His book peaked my interest recently because in my career from graphic designer, web designer to web developer, I have always been told that as far as aesthetic design goes:

"You're just making something look pretty."

But Dr. Norman tells us differently.  Major take aways right off the bat:

• Two Japanese researchers tested usability of the same ATM application one simply more aesthetically pleasing than the other.  They found that the interface which simply looked better produced better usability results.
• Doubting the study, an Israeli scientist took the same study, translated all the Japanese text into Hebrew and ran the study again.  Bolder results confirmed the original study.
• Attractive things work better because it:
  • Affects our effort - We as humans become emotionally attached to aesthetically pleasing interfaces so we try harder to make it work for us.  We like the inteface so we keep trying even if things don't work the first time.
  • Affects our ability - Aesthetically pleasing interfaces put us in a better mood which in turn affects our ability.  If we are in a better mood, problems appear easier to solve and alternative solutions arise easier than in a negative, nervous or uncomfortable state of mind.
  • Effort and Ability Affect Performance - It makes perfect sense that further effort and better conditions to improve our abilities will result in better performance.