If it's www.google.com the word will be considered more relevant to the search (will come higher positioned) if the accent matches.
And I think they do well, because some words differ only in terms of accent from language to language. For example, "inglés" (Spanish) in Portuguese is "inglês", "formula 1" (English) in portuguese is "Fórmula 1" etc.
But when it comes to www.google.com.br (Brazilian Google) it makes no difference. The results are exactly the same no matter if the Google user types the graffic accent or not.
So my advice is, if you're concerned only with your public, from your county, using your country's version of Google, do put all the graffic accents. It will look better (will not look so carelessly) to the visitor and they will get there the same way if they don't type the accents on Google.yourcountry .
Considering, of course, that your country's Google ignores graffic accent just like Brazilian's does! (Check that searching for something both ways)