In the early days of the internet, the Keyword Meta Tag was the most important information used by some early search engines to determine relevance hence ranking. However, that was the past. Now, the keyword tag is ignored by most search engines due to the abuse.

So it doesn't matter if you use the keyword meta tag or not. However, if you do include, do remember be careful not to repeat any word and include only your most important keywords - those that you actually use in the content. 

The meta tag that you should be concerned about is the Meta Description Tag.

Here's how the meta tag looks like when you view source:

<meta name="description" content="One or two sentences to describe the page consisting of keywords">

The words in the description will be used by the search algorithm to have a snapshot of your web page. Furthermore, major search engines such as Google, Yahoo and MSN Search results are displaying this description when you used the keywords here.

This is important because a well written description will attract the search to click and come to your web site. This small but important detail is often overlooked by most webmasters and web designers.