Ten years worth. At least.
Today, at TechEd, Andrew Lees announced that there's a new policy for *all* business and server products (highlights mine):
This announcement affects the Support Lifecycle Policy for current and future Visual Studio and .NET Framework products. Current and future developer tool products are now eligible for 5 years of Mainstream support, and 5 years of Extended support. In the past, these products were eligible for 5 years of Mainstream support and 2 years of Extended support. Mainstream support includes support options and programs such as no-charge incident support, paid incident support, support charged on an hourly basis, support for warranty claims, and hotfix support. Extended support often includes support charged on an hourly basis and paid hotfix support.
I hope this means that no one feels left behind (gee, that would be a great slogan — I should think about using it elsewhere)
TTFN - Kent