Sony has virtually zero chance of outselling MS in the US outside of the next 4 weeks or so. Once ODST hits, it will be MS back on top. The holidays will handily go to MS because of the arcade bundles that are sure to come. $299 is still way to expensive at the moment.
In 2010, MS will probably bury Sony (and possibly even Nintendo) with Natal.
OUS, Sony will be ahead for the rest of the year. However, when Natal launches it will be up for grabs, although I give MS a better chance of winning EU than Sony. Japan is a foregone conclusions so it isn't worth talking about.







