Avoid using the "latest version" reference. In order to ensure that it's serving the latest version, it serves the script with an extremely short expires header.
Not to mention that referencing the latest version means that your code will be untested against anything but the library version you built against.
Keep in mine that many sites use the Google version, so if you do to, some of your visitors will get it "free" (from their local cache). The caveat about not using the "latest version" stands. And for the gods' sake don't use the actual google Ajax loader API, it's an extra script to load. (Include the above URL directly, not by doing a .load() on something else.)