While I wouldn't drop existing support (unless it causes problems), I'd rather see these sort of fixes out of the main codebase. That would make it easier to take them out in the future when it makes no sense to keep them.

We should also decide on a convention for dropping supporting code for old browsers. At some point it just makes no sense to carry old code anymore. For IE, the convention could be when the last version of Windows that supports that version of IE has reached end-of-extended-support. For IE6, that would be 8 April 2014 (Windows XP end-of-extended-support). For IE7, that would be 11 April 2017 (Windows Vista end-of-extended-support). For IE8, that would be 14 January 2020 (Windows 7 end-of-extended-support).