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I think you are looking at this the wrong way. A subdomain should warrant enough unique content that is related to the main topic of your site. Links to both a subdomain and folder will increase value of the TLD. In regards to "link juice" - building on the TLD will always help. You should be looking at this from an ease of use perspective of your readers. Point is, I have yet to see any difference from a subdomain vs a subfolder. I've never seen a subdomain have a higher PR than the TLD, and same goes to the subfolder idea as well.

hey Steve, are you still standing by what you said above?

Create a regular and mobile site map, then remove the redirect for the googlebot (authentication google bot that is not just the googlebot useragent as that is easily spoofed). As a side note, anyone looking for mobile device redirection, detectmobilebrowsers.mobi should only be used if you are a small business within the US or Europe only.  If you are a medium to large business and/or care about global visitors and covering all mobile device not just top of the range "smartphones" its simply not good enough and you should look into using WURFL or "DeviceAtlas".