Web design is quite important to identify who you are (in terms of web sites).
Take for example, Maybank2U has changed it web design since last year and people are complaining all over. It is better design, to reflect latest paradigm but somehow it managed to make people disturbed. I am a user.
Another example is TheEdgeDaily which just changed its web design.
Which I still haven't got used to it. The impression that I am reeling on is that TheEdgeDaily now has got no news and they are now into the Start Page business.
So, the web design is important for your users and also as a way for them to live on.
Look at the big 3 (Google, Yahoo, MSN), they haven't really changed any of their web designs since 10 years ago. Google is white, Yahoo is red, MSN is blue.
For searching part, Google is good for technical search, Yahoo is good to backup Google in case you cannot find satisfactory search result and MSN is good for lifestyle search.
For application, Google is good for technical tools, Yahoo is good for applications and MSN is good for contents.
If each of these 3 big guys suddenly changed strategy, the Internet world will be disrupted. Web users will be subjected to sudden culture shock.
Think about Google, the moment they decided to change the plain home page, people may stop using the search service.
Learn from this as best practice, which is to use workflow and interface (as identity) to capture the heart of users. All these premise on a simple foundation; users are dependent on technology and even designs.