If you login to Google Webmaster Tools and go to the "Keywords" under "Your site on the web," Google will show you the "most common keywords Google found when crawling your site." In fact, Google said, these keywords "should reflect the subject matter of your site." But what if they don't?
A Google Webmaster Help thread has one person complaining his blog shows the months of the year as being his most common keywords in his report. What should he do?
Googler, Jonathan Simon replied saying:
I took a look at some of your site's pages and found that month names are fairly prominent on your pages especially when there are comments (where each comment has a month name associated with it). You could modify the date format associated with comments so that dates are displayed in a different format like MM/DD/YYYY but I don't think you should really spend your time worrying about this. A better way to address this issue would be to focus on the keywords in the list that are representative of your blog's content. Consider how your blog includes those Keywords and do something similar for other keywords that you'd like your blog to be associated with. I find it's helpful to view the Keywords list in combination with the queries (reported in the Search Queries section) which are generating impressions and traffic for your site. If you see queries that are bringing your site lots of impressions but only few clicks and find those same queries aren't listed the Keywords report for your site, then that information should assist you in prioritizing your efforts when you're considering adding new content to your blog.
Maybe this comment can help others?
Forum discussion at Google Webmaster Help.