The styles were change to comply with microformats that will improve the website SEO. Image store v3.1.0 was out for testing for a month many people helped improve it and provided feedback and they got a change to test it before moving it into their live sites.
I have suggested on my blog and some forums post to follow me on twitter, google plus or RSS on news for mayor upgrades and that way we can provide backwards support as much as possible and give you a chance to fix anything on the site that needs to be fix before moving it into production.
I am really sorry that you need to re-style your site, but for mayor upgrades I always recommend testing it on your development sites first. To temporally fix your problem you can reinstalled version 3.0.9