First of all it patches the browser check issue, it seems that Firefox 3 is handling the OR operator in regular expressions in a different better ? way than any other browser ...
If you were using the checkIE property you should be aware that it isn't anymore working as excepted before.
The default value in 1.0 was 'MSIE 5\.5|6', it is now 'MSIE 5\.5|MSIE 6'
We also introduced a new feature called 'scope' for the hackClass and the hackExtension methods, this parameter permits you to define a starting node to hack all his children.
This is very useful if you don't want to hack the full document but just a defined part of it.
Bye !
Links :