I've put up 12 articles on Web 2.0 properties such as Vox, WetPaint, HubPages etc. Just about all of them are indexed by now but not even showing up in the SERPs. My landing page is #59 in my niche which is fine for right now. None of my Web 2.0 props are ranking and they don't have duplicate content. I did summarize or spin each article so that they are not the same. However, my URL is the same - for an example - for Vox, I would have abc.vox dot com - for wetpaint, I would have abc.wetpaint dot com - and so on. Is the reason why I'm not ranking w/ my Web 2.0 properties is because my url is really the same - even though my content is spun? btw...I'm just aiming in one niche, so I'm really concentrating on a three word phrase as my KWs (at least on my Web 2.0 Props).
I don't think the subdomain of the URL will make a difference. It takes a while to rank and you will also need a few decent backlinks to the Web 2.0 pages. There was a time when they would rank on their own, but it's harder nowadays.