From a quick reading of microformat's it is not just a case of a single line, but having descriptive class tags for the relevant contents on all of your pages. I doubt just adding a single microformat line on the home page would effect search engines much (as that would make it too easy to SPAM search engines).
It is entirely up to you as the whether you want to implement microformats. Do a search with your favorite search engine for terms such as do microformats help SEO and make your own determination. From my own reading on it, it may not help SEO, but it won't hurt either. The only downside is maybe having a little bit of extra overhead by having a few more class tags in your HTML.