I thought I would blog about my personal experience with this very question, about 3 months ago I found many so-called SEO professionals that were claiming that the Meta Keywords and Meta Descriptions were now redundant and should be removed due to the fact that search engines could now cleverly devise a list of useful keywords, and the description would be taken from the page content itself - meaning better SEO and happier Google if you removed the offending tags.
THEY WERE WRONG!
Well at least in my case they are, In November I decided to bite the bullet and I modified resplace.net so that it no longer output these two meta tags, the logic was that if these SEO Professionals were correct, absolutely nothing would happen and stats would continue to run smoothly (as they have for almost a year now with only minor increases over time). However in reality I found that within a week my stats more than HALVED, I panicked but kept my cool and rode the storm hoping that it was just temporary while Google refreshed the content and my search positions, this never happened and after 3 weeks I decided enough was enough…
Fortunately after changing the system back so that keywords and meta descriptions were back in the pages, my stats instantly regained consciousness. FEW!
So be warned and don't listen to these so called “professionals”, try their recommendations but don't expect it to be right, what works for some people, might be suicide to others. So be prepared to have to revert back any changes you are trying.
And remember, Google can actually take up to 2 weeks to update it’s system to your changes, and during this process you may see a drop in stats, but stick with it for at least 3 weeks to see the true result of any changes.