Been a couple years since I made my living on the net. Used to spend 60K a year with Adwords with great conversions. Got burned out on the net and went back to brick and morter, a niche manufacturing business. Finally got around to putting up a site and and optimized a page for adwords. I am getting the clicks but over 60% do not stay for more than 1 second. WTH? This is very targeted. Trust me on this. Why would someone click and ad and then backclick before seeing the content? Only thing that comes to my mind is maybe the page is jpeg heavy. But it loads fine for me in cable and DSL. I just can't believe there are people out there searching and clicking without exploring their clicks. Least not over 60% of them.
Where does the 1 second figure come from? From Google or a stats package or what? With a typical web page, you have no way of knowing whether someone looked at it for a second or an hour. All you can say is that the user didn't go any further.
If people are actually backing out before the page has even fully loaded, I see 3 possibilities off the top of my head: 1. Page too large, a possibility you have noted. 2. People are not seeing what they hoped to see when clicking on your ad. 3. Bogus clicks, and poorly disguised ones at that.