there's not a golden "text-to-ads ratio" or a word limit for ranking
I realised that several weeks back when one of my sites started climbing the G.co.uk SERPs and many pages are now top 3. All these pages are constructed the same with product name in the titlebar, meta description, on-page product name and the product 500 x 500 image, nothing else.
It's a retail widget site purely for simple informational purposes, it's not designed to do anything else.
At the same time I have a trade widget site which I have been experimenting with during Panda. These product pages had some informational text on them and were pandalised but not heavily. Subsequently I have beefed-up the information on them, tightened-up the SEO and ALL those pages are now back in the top 3 of G.co.uk.
I have my own theory as to what, and how, Panda is targetting specific sections of my two biggest sites and I'll be experimenting with that soon however I know, for me, that it's nothing to do with perceived crap, ad blocks or site construction.