I'm having problems on Google for some of my sites, so they rely on Yahoo & MSN. For my sites that do well in Google, that is where most of the traffic comes from.
At the moment, it's still google which contribute the bulk of traffic but I expect the percentage coming from Bing to increase further. Looking at the way the progress Bing has made, I think it's quite possible for them to be almost at the same level with google.