Marketo's costs for enterprise level service requires a long term bet. The company I work for has invested millions in Salesforce integration but 8 months later I've received 1 lead which was dead wrong.
Our industry doesn't lend itself well to social marketing so that may be part of it, but I wonder how many businesses will actually see a return from using Marketo. Executives stuck in the sunk cost fallacy will keep them going for a few years even in their worst accounts. Their market presence is so recent that their retention rate has nowhere to go but down.