Since all code is not treated equal among various web browsers and operating systems, web developers have to decide which browsers they want to cater to and attempt to develop code that works perfectly for their target audience. For the remaining browsers, we simply accept that you can’t please all of the browsers all of the time.
Dave at Mezzoblue posted a handy list of browsers that he attempts to cater to. I think it’s a good list, though in practice, I often cater to even a shorter list than this. Perhaps it’s time for me to raise the bar.
On a similar note, TheCounter.com offers a good guage of what web browsers are actually using. Sadly, IE-flavored browsers are still used by more than 93 percent of those on the web.