There is always a debate on whether these are worth investing in or not. Whatever the side of the argument you are on it is worth having the ability to create and display these tags well.
WordPress is a wonderful tool but has some out of the box deficiencies. The creation of meta tags is one but this can be addressed by adding plugins which extend the functionality of the core package.
One plugin I have adopted is the excellent Headspace2 which is modular and gives you the ability to control many aspects of your code as seen by the search engine spiders.
Have just fitted it and am test piloting the plugin for a while … I will report back in a week or so on progress.