Meta Tags cannot drastically improve your SERPS.
But yes they make a difference.
For example, without meta tags WMP would show in google with this description:
But with meta tags:Welcome to Webmaster Peers, an up and coming community where......
I can make the description as I want with meta tags.Webmaster Peers is a friendly and experienced community for all website owners!
And I believe meta tags make a difference as I had AviationEarth.com.
Most of the articles were from Wikipedia :P (i was just 12 then). I used the meta tags to change things, and I ranked above Wikipedia for some articles...so yes they make a difference.