aakk9999 - 5:37 pm on Mar 15, 2010 (gmt 0)
I am following this discussion with interest because I am in process of changing from ugly dynamic URL structure to "friendly URL" structure. The site has around 3000 pages and we will change probably 300 of them in total, leaving the product data having ugly dynamic URL structure.
Started slowly changing selected pages about 5 weeks ago and so far only one page dropped ranking for a few places, the others retained or improved.
I have to say that one of reasons for change is to be able to target specific countries using folder structure (the site runs in number of languages), and therefore it could easily be that any loss of ranking has been compensated by advantage gained through geo-targeting.
We have also changed few english language pages (english language is not geo-targeted)but have seen only one drop of ranking, other pages have retained it (so far).
It perhaps helps that pages being changed have very few inbound links and internal linking structure has been changed to point to changed URLs?