There is always the possibility some CBS executive will decide they want to try and monetize some part of Cnet. Cnet wasn't exactly doing so great on its own before CBS bought it, and I doubt it's been much of a money maker for CBS since then. I'd personally argue it's because CNet had a habit of buying up sites, and then redesigning them to make them nearly impossible to navigate, driving away a lot of the regulars. What became tv.com is a great example. It was a fairly simple site, the Cnet turns it into tv.com with all kinds of pointless scripts for ads and bogs everything down with huge high resolution graphics, and pretty much every other trick no-talent web designers come up with to try and mask their general ineptitude.
So, there's always a possibility, and if that possibility concerns you, you probably should reconsider using any service you wouldn't be willing to pay for tomorrow. Or at least any service you wouldn't be perfectly willing to give up tomorrow if it became a paid service. That goes for any site, not just Cnet. For the longest time I resisted using the IMAP function of Gmail on the off chance that Google may decide to start charging for it. I recognize that they might decide to start charging for that at any point, which they've made no secret of, and I am prepared for that eventuality should it come to pass. You should be similarly prepared.