IE6 will officially die six years from now (i.e. it will finally be completely dead in 2016). It is mathematically proven by this chart:
(Download Excel Spreadsheet)
The data comes from the W3C Schools browser statistics page. The "Months from 10.2% Overlap" is referring to the two points where browser usage of IE5 and IE6 were both at 10.2% (time-shifted so you can see how similar the data is). The W3C site appears to stop tracking browsers at 0.5% (I'm calling that dead). My goal with this chart is to show that the data is rather similar at this point in time.
Six years is a pretty bleak outlook. I also had Excel fit a line to the chart and came up with "y = -0.0093x + 0.085" with a R^2 of 0.9854 (a slightly better fit with the available data nodes). With the line, IE6 is declared dead by the W3C Schools' standard of 0.5% in 8.5 months. So, the real answer is probably somewhere between 8.5 months and six years. I'm leaning more toward five years. Come on - that's a curve and we all know it. It won't matter how many websites put up "You are using a dead web browser." People clearly are ignoring those signs and only upgrade when they want to.