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I think Businesses.pro is a solid registration. The downside is obvious. Business keyword domains are very rarely sold in plural form. I can find one notable exception, HomeBasedBusinesses.com sold for $23,000 in Oct 07. That's a foul mouthful as a brand but presumably a nice little PPC earner.
Businesses has excellent goodness of fit with the .pro extension so I don't see why you won't be able to sell it for $X,XXX+ in 1-2 years if .pros gets cheaper to register. and restrictions are removed. Right now low $XXX.