I run a travel and accomm booking site. It's a legitamate business that earns over 350K per year. The old site was in HTML and had seved us well for about 3 years. I had designed this site myself as the business grew from $100 per week into $1000 a day. But I ain't no web designer. It was definately time to put the best and most professional site out there that we could. this would also save lost of labour time for our staff. I put the job up on freelancer.com and also approached local designers. The local designer we chose wanted to do it in .aspx - not the .php I was really after. After a month of developement the site went live last Friday. As of today I have now got either all my rankings back or improved. I was really sweating on what kind of dip we'd take - as we need that daily income, and couldn't afford more than a couple of weeks in the wilderness. Now the things I did with this in mind were Approx 5 facebook posts from 5 differnt accounts to roughly different 10,000 people. - this got every account banned. All the posts were directed at www.xxxxxx.com/index.aspx - rather than just www.xxxxxx.com Bookmarks to every interior page - the whole lot. These were done to both the Code: [URL="http://www.xxxxxx.com/store/products.aspx?categoryid=b404dd1d-0cbd-4cad7-8e223-5f1c7c60ae36"]www.xxxxxx.com/[U][COLOR=#0066cc]store/products.aspx?categoryid=b404dd1d-0cbd-4cad7-8e223-5f1c7c60ae36[/URL][/COLOR][/U] versions and the plain english urls. This long list was then blasted with every autoapprove SB list I have. Hitting google with a new sitemap every day - this sitemap did change as new pages were published every day. Funnily enough the aspx coded url's are doing just as well as the plain english - something I didn't really expect. My main 2 keywords, which are very very competitive did not budge once - they are directed to my home page, so the address didn't really change. I tried to keep the content the same where possible, although this was not always possible as we were trying to improve the useability of the site - I don't think I lost anything due to the changed content. I haven't optimised the images yet - so the site is very heavy and loads much slower than before. this didn't seem to affect us, so much for page speed in googles eyes. So if you are thinking of a big redesign but afraid to because of rankings, I think I've proved that a painless transition can be acheived.