Every webmaster and web-developer knows:
Having to design a website compatible with Internet Explorer 6 is a hassle. Horror.
Microsofts IE never was really folloed web standards.
Back when IE6 was used, that was (probably) the time when websites were laid out with tables.
Today we have css to seperate design from content/markup.
This also reduces overhead, is a lot clearer in code, improves markup and thus search engine indexing a lot/understanding.
IE6 fails with all those technologies.
Although it’s slowly dying there are still ppl using it. Because they don’t know better.
But it’s really time to upgrade. Really!