I consciously prefer serving it myself rather than google because if it's a first time visitor, he will be requesting other static files as well from the site, so having a cached copy of jquery leads to minimal loading time differences (although it does save on bandwidth).

However if there isn't a cached copy of google's jquery there is the overhead of a dns query and new http connection to google.

This compared to the already open keepalive from my static server increases load time dramatically.

First impressions count, and you have few vital seconds to make a good one.