Another good post for Gerry McGovern at Giraffe Forum about why if you think you need to redesign your web site, you may have a deeper problem:
Website redesign is nearly always a bad idea because it reflects a project-based management approach. The best websites are not managed simply as projects but rather as processes.
A website redesign approach is usually embraced by organizations who are reacting to the fact that their websites have fallen into disrepair. Something is not working and the belief is that a nice redesign, some nice new graphics and colors, and perhaps the purchase of some fancy content management software, will solve it.
This approach is papering over the cracks. The cracks are a lack of resources to professionally manage the website on a day-to-day basis. The cracks are a lack of genuine customer focus, and a lack of continuous testing and evolution. The cracks are a lack of a rigorous review process to ensure that only quality content remains on the website.
His point, of course, is that if you aren't keeping your web site up to date - in tune with the needs of people visiting it - a big redesign is not going to help, because down the road you're just going to have the same problem.
Gerry says that redesigns are "almost always" a mistake; I wouldn't put it that strongly, but his point is well taken. While there are sometimes very good reasons for a big overhaul, if you let the last fantastic new web site turn into a mess, what will you do to make sure the new one doesn't suffer the same fate? Make sure that if you feel you need to do a redesign that you are designing a new process as well as a site.
As always, one must keep site users in mind. When you go to a familiar site and find that it's been transformed, you probably don't think, "Oh, goodie! Everything's in a different place now!" The disruption to your regular visitors had better be worth it.