It's the whole package that matters

From Nielsen’s latest Alertbox column:

The websites that had high visual-appeal ratings were then tested for usability. On average, participants’ task-failure rate on these sites was over 50%; this is an unacceptable failure rate based on our tracking of failure rates since 2000. However, despite this atrocious failure rate, participants’ satisfaction ratings remained high. In this case, research indicated that the look and feel of the site had a Halo Effect on the entire site experience, even when these sites were poorly designed for usability.

Usability on its own might fall short if your design doesn’t connect on an emotional level. Things that look better also work better.