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If I were going to disallow something I would go with noindex tags. The robots file is perfect with just those 2 lines. Then, there are some plugins that will help you avoid any SEO issue like SEO by Yoast. Personally I like to noindex,follow tags, categories, and archive pages, that's it. But again, noindex, follow with a robots tag on the page, not using the robots.txt. SEO by Yoast will make that as easy as it can ever be with just a small configuration steps. Give it a try, you can always disable plugins Wish you the best!

Moz has a very comprehensive list of recommended firms here: [http://moz.com/community/recommended].  I can't personally speak for any of them, but the list seems well researched and vetted.  Hope this helps.

My pleasure.  I've done it before too.