rocknbil - 4:20 pm on May 10, 2012 (gmt 0)

<focus, just SEO, just SEO . . . >

Off the top of my head the only place I can think of that ID's or classes might be relevant is in the use of microformats, and even then, only indirectly. Microformats are often used by some services (local listings come to mind) and if your site does well in those services due to proper use of microformats, then that site will likely lend you link juice that will help your overall results.