It depends..

If you feel that you really need a sitemap, I think that most sites don't need them, then you should go all the way..

If you have signed up for Google webmaster tools then you should register each subdomain on it's own and verify each subdomain.. They can all be under one account.. This will help you with link tracking and some of the other tools that wmt offers.. You can then create a sitemap for each subdomain and point them out in wmt as well..

Each subdomain would be, and should be, treated as it's own site as far as Google wmt is concerned.. This may add some more work to your plate depending on how you generate your sitemap.xml files, but in the long run it might be worth it..

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Steve : Animal Charms Animal Jewelry | Fishing Blog
I'm smelling a whole lot of if coming off of this plan.