If you have a large number of elements with delegated events attached, and the original bound element also has other delegated events, performance in IE 7/8 (I haven't tested 6, and 9 is fine) is much slower than it used to be.

See the following tests:

http://jsbin.com/iyacim/1/edit (1.7.2)

http://jsbin.com/uxovuh/1/edit (1.8.1)

When you click on any of the spans saying "Click here", a red box will appear instantly in 1.7.2, but it takes much longer to do so in 1.8.1.

This still happens if all the click functions return false.