Be careful with browser detection

If you need to use some kind of browser detection, make sure that it doesn't break when a search engine spider (or any unknown user agent) comes along. If the spiders can't get in, you won't be found. I've seen this happen on the sites of fairly large companies.

Pages that depend upon a specific browser tend to be flawed at the most fundamental levels. Most sites do browser detection badly. Most sites make the incorrect assumption that the UserAgent string can be trusted. Use of browser detection should be function specific ("Does this browser know about getElementById()?") and then only when there is a specific need. Entirely too many sites say "Netscape X or later" and fail to support later, fully Netscape X compatible versions of other browsers.