How often should you redesign your site?
patio11: Test constantly.  Button placement, calls to action, colors of buttons, etc -- 5% increases to conversion compounded 20 times means big bucks.As for total throw-it-out-and-start-over redesigns: I'd say "seldomly".  I did one once, because I had the golden opportunity for it -- both a major tech change that was going to require a code rewrite, significant technical debt in keeping up the old templates, and major feature modifications which forced a rethink of my information architecture.  As long as I was going that far I figured, eh, what the heck, get it a totally new look as well.I was surprised that for all the extra work added and the professional design, conversion rates moved less than when I tweaked spacing on buttons a little bit.  Ahh well, that's the way the cookie crumbles.  The non-design aspects of the relaunch proved worth their weight in gold.(I was also totally prepared to send the designer a check and a thank-you card and not use a single pixel of it if the conversion rates changed in a majorly negative direction after the switch.  Thankfully the starting hiccups were not that bad.)[Edit: incidentally, sub-sections or mini-sites are a great way to beta a design against your visitors without having to put your existing relationships or numbers at risk.  When I made sweeping changes to my site, the sweeping changes started out on a "brought to you by this other site" mini-site that I set up, and I did iterative improvement on things like button placement and calls to action over there before I integrated them with the oh-goodness-if-I-screw-up-this-will-cost-money site.]