JQuery Browser Rejection
plugins.jquery.com
plugins.jquery.com
For read-only sites, fine. But IE6 could cause some serious problems for many web apps that haven't properly been tested for them.
Then there's the activism angle - only by applying pressure, one site at a time, can the IE curse be gradually eliminated. The total wasted man-hours catering to its quirks is exceeded only by the hours wasted producing weapons and religion. sigh
If you must filter then best done at the server in my opinion - then you can render a page that is tailored to the specific circumstances.
When forced to deal with frontend stuff, I have wasted more hours of my life than I care to count at least trying to get basic rendering in IE6. While it probably won't get most people to change it, at least making them aware of the fact that their browser is ancient might wake SOME up.