One of the real headaches for website designers is the variety of browsers out there, meaning that we have to ensure that a website looks and functions in different browsers.
I recently was reviewing the browser usage stats for 2009 and quite surprised to see that IE6, 7 and 8 are being used almost equally, you would expect that people would upgrade their browser (as its free and normally better and more secure) but some months the usage in IE6 actually increased slightly. IE and Firefox are the main browsers, Firefox is the web designers friend due to its plugins and customisation, but Google Chrome (the new boy) finished the year with a near 10% market share.
I entered my internet life with the choice between Netscape Navigator and Internet Explorer when Freeserve, Yahoo or Alta Vista were the home pages of choice. We now have much more choice and much more complexity to deal with to ensure that a website is functional and beautiful for as many users as possible.