According to the latest browser statistics (link below), the IE6 has a 17.1 market share. How many of those folks may care about the Web2.0 platform we are writing? May be about a fifth? So overall for those 2-3% of the entire market, is it worth spending your valuable cycle, which you would rather spend on features of your site. (also save on Tylenol expenses)
You have <i>no idea</i> if a fifth of IE6 users will use your products: for all you know they could <i>all</i> use it.<p>My advice: support IE6 entirely, launch, iterate, then once you have users (= market) then make the choice to scale back IE6 development.<p>As a young startup you'll have plenty of reasons why users won't stick - don't make browser support (eg, something you can fix and are aware of) another reason.
If it's easy, dedicate a little code to give them a reasonable experience. But any substantial effort in that arena would be a waste of time: Focus instead on creating a great product that will bring forth a few more people who use updated browsers.
As a data point, we see 53% of our traffic from some flavor of IE with a breakdown (for IE) of:<p>IE-6 / IE-7 / IE-8<p>39% / 55% / 6%<p>For us, this sadly means that supporting IE-6 is mandatory.