It's pretty simple– if you want to support IE<9, don't upgrade to jQuery 2.x. A lot of people are already dropping support for IE<8.

It's really not that simple. Now you have to check to see if a plugins support 1.9 or 2.0, and plugin writers will have to support both or IE8 supporters will have to live without new plugins.

The article specifically states that 1.9 and 2.0 will be API compatible. So no, you won't have to do anything other than include the proper version and forget about it.

well they do provide 1.9 to handle that, this is is how they recommend you handle that

<!--[if lt IE 9]><script src="jquery-1.9.0.js"></script><![endif]-->