Being in the web development business, it's always important to make sure that our clients' websites render/present themselves appropriately in all the major browsers. Too many times website designers have great looking site that appears "functional" in Internet Explorer or Firefox but neglect to take that next step to do browser testing to ensure proper website functionality between all browsers.

Based on the latest market share reports by AXIIS, here is the most recent browser market share breakdown:
Firefox - 47.0%
Internet Explore 6 -11.1%
Internet Explore 7 – 13.3%
Internet Explore 8 – 13.3%
Chrome – 8.5%
Safari – 3.8%
Opera – 2.3%

Because most web users don't even realize that there are differences in the way that different browsers render pages, few people take the time to switching to a different browser in order to see if sites they develop render properly. Every company's goal is to have a great looking, professional site to be proud of and taking the extra step of browser testing is a little detail that makes a big difference.

Sources: http://www.w3schools.com/browsers/browsers_stats.asp, http://www.axiis.org/examples/BrowserMarketShare.html