Dublin Core is a would-be standard that never caught on in a big way - and Google isn't using the DC meta data in their algo as far as I know.
I've worked with sites who do use Dublin Core, and in all the analysis I've done for them, I saw no sign of any effect on their search traffic. Though it's been many years, I also remember Matt Cutts saying pretty much the same thing.
So I'd say suit yourself and your own needs. It will neither hurt nor help you with Google.
[edited by: tedster at 4:30 pm (utc) on Oct 21, 2010]
i have not seen any significant benefit of dublin and most other meta data. google's ranking algo places much more importance on links and visible content. i would focus on those two areas before worrying about most meta data.