Ok, here's my take on some of the dissenting opinions expressed so far.
There are a couple ways to look at browsers in your stats.
1) What Browser are they, the surfer, using. This is good thinking. Know thy surfer (spelled CUSTOMER) and make your sites
work with their browser. Thinking that only the newbie surfer sheep running on MS IE are your only viable customers is just plain ignorant. There are hundreds of thousands, probably millions, of horny surfers with open wallets that just plain hate MS IE. Maybe they come from the old Netscape school and when it became Mozilla they kept with it rather than going IE. New to the web doesn't mean open wallets anymore. Your BEST customers are likely more savy surfers that Know What They Want. Just because they "only" represent 10% to 25% of your customer base are you willing to throw them out? If so, PLEASE, PLEASE send them to my sites.
2. What Version of a given browser are your surfers using. If you see MS IE v4 or older or Netscape 4.x or older then Yes these surfers are likely not viable customers. The reason being if they aren't willing to keep current, at all, with their OS and accompanying software on their own computer(s) then they probably aren't worth the time it would take to create a marketing campaign for them - even IF they could view your sites to begin with.
As a business owner I am hesitant to disregard even 5% of my potential customer base - that's 1 out of every 20 people that visit my store! Imagine if BestBuy were to based upon some archaic algorithm of demographics it ignored every redhead that entered their stores. It's hard enough to get good ratios without self-imposing limitations on your own prospective profits.