Since Microsoft stopped publishing their IE6 compatibility VirtualPC images, I've stopped testing sites in it. IE7 and up are supported, though things look prettier in IE9+.
P.S. I publish W3Counter's monthly browser usage share reports. Across the ~60k sites W3Counter tracks, IE6 is down to 0.7% usage.
As an example, the last company I worked at, our main customers were home contractors and other DIY type people and IE7 was a large portion of the market share.
My best advice is to build a product and check analytics to see how many customers are actually using older browsers. If it's a small group, its probably not worth the effort to make sure everything is ported over. Sometimes it can also be difficult to test older browsers without spending a bunch of time setting up VM's.
For my own personal projects, I dont even fully support IE7.
IE6 is around 0.4% of traffic so no, we no longer support it. Even IE7 is barely being tested (3%), only if users complain will we take a closer look at fixing things for it.
So far this year, no client asked for IE6 support.