Is there any benefit of Google Analytics asynchronous tracking code if it isn't placed in the <head>?
Compared to having the old tracking code at the bottom of the page, having the asynchronous code at the top of the <body> should still mean that the tracking is more likely to register users who leave the page (or interact with elements on the page that are being tracked) before it has fully loaded.
You can put it anywhere you just get the most benefit from putting it in the header. The full instruction to add it to your web page are here - http://code.google.com/apis/analytics/docs/tracking/asyncTracking.html.
You do want to put it inside of the head or body tags though. Just to be clear. But beyond that you can do whatever you want.