enigma1 - 12:15 pm on Feb 1, 2012 (gmt 0)
You cannot get below 45% but on which page? Typically the more the page deviates from the site's content the higher the bounce rate as ppl won't find relevant info.
For instance with a shopping cart the checkout pages may show a very low bounce rate. A badly structured home page may show a high bounce rate. Also what are you using to measure it? Some custom tool, GA, Alexa etc.
Also you could have some highly irrelevant pages in your site but with a high CTR and this could influence the average rate.