Rahul talks about web standards, usability, etc. I have to agree with him on this.

Today, web browsers do follow standards, and it should be easy to ensure a webpage works on them. Moreover, Mozilla Firefox and Opera can both be installed easily on Windows machines (Safari can’t, but its parent, Konqueror, can be installed under a unix-like environment called CygWin). Mozilla Firefox alone commands over 10% of the market, and the non-Microsoft browsers put together approach (or perhaps exceed) 20%. These browsers also allow easy scaling of fonts and setting of font-family and font-size preferences. It is, if not idiotic, at least completely irresponsible to choose to test only on one web browser, MS IE, and that too only on version 6. With the release of (and, often, enforced upgrade to) IE7, many sites are now broken and need to be fixed; they need never have been broken in the first place.

Thanks to Space Bar for the hat tip