It matters mish!.Keeping in mind the future scenario of web standards XHTML that demands lower case tags.We should use lower case tags...definitely!!
It will be the other way around. Implementation will be adopted by Presto, Gecko, webkit & derivative engines long before the standard becomes a recommended specification by the w3c. http://blog.whatwg.org/faq/#schedule
Of course, leave it up to Matt Cutts to recomend presentational markup to semantic markup (if what you're saying is true, that is). And people wonder why I don't do SEO for SEO's sake. @Adam, I was being (somewhat) sarcastic with my previous response (about implementation).