Here's some less-than-great insights into what I'm seeing on my end. First, this is a screenshot of the style recalculation that the jquery.ui.position script makes:
The browser seems to be doing some optimization that's making the exact action that causes the recalculation non-obvious. This second screenshot shows a layout recalculation that's performed immediately after the style recalculation:
When I minify the JS, the exact line numbers or calls that cause it get a little fuzzed. I've got some unstashed changes that I can't clean up at the moment, so I can't show stats from my dev environment with a very heavy page layout (where the cost is a *bit* more than 2ms). I'll try to post something a bit later today or tomorrow morning that will hopefully make the issue a bit more visible.