I realise the high exit rate concept may only apply to ecommerce sites, but whatever type of site you have, I think if you look at the PROPORTION of the pages people visited with high and low exit rates (low I would say is under 30%) there will be a pattern.
If you have an ecommerce site and 30% of your pages have an exit rate of 80% and those pages are product pages, you have a quality problem.
I'm literally working through this now on our site, keeping in mind Amit Singhals Guidelines and I am amazed at how many of the guidelines suddenly make sense when I look at my high exit rate product pages (similar products, rubbish products, badly decribed products, overpriced products, products that don't sell.....they ALL have higher exit rates). People don't like these pages and they leave the site, having been elsewhere on the site beforehand.
Some cases are proving to be not so clear, but when I also look at Average Time On Page, Unique Page Views and Entrances whilst physically looking at the page, I get it.
There must be a pattern for other types of sites. It's all about the proportions. If you have a large proportion of pages showing statistics you would not expect for those types of pages, I think that's why you have a Panda problem.