I have a site that presents information in each page with HTML tables. Does this affect my site's SEO? Should I replace all tables with divs?
I'm not using HTML tables for layout. I'm only using them for representing information.
No, this will not harm your SEO. Using tables for layout is frowned upon for various reasons but that doesn't mean you're never supposed to use them. They're meant to be used exactly as you're using them: for tabular data. If anything, this will help your SEO as it will help search engines understand your content better since your markup will be semantic.