According to this MarketingProfs study conducted with CMOs they claimed that, in-house marketers (44%) and clients (26%) are the chief drivers of innovation in marketing for companies. This is odd because it is totally counter-intuitive to the wide ranging belief that agencies provide more innovation. The argument is based on the idea that at a marketing agency you get to try things out across different clients and that you are surrounded my "marketing people" all day, and therefor you it is more likely that you will be innovative. As opposed to the in-house person, who's creativity is stifled by business cases, internal politics and reporting, and the fact that they are not in an environment that is conducive to marketing innovation.
However, having now worked in both worlds I can see what this study turned out the way that it did. As an agency guy, it was difficult to educate and get buy in from clients on innovative new techniques. Not only that but clients want execution on sure things. They want to know that their marketing budgets are going to yield and ROI. Whereas as an in-house guy, I'm encouraged to try new things and if I fail on a campaign it does not mean that I lose my job. If companies had a different attitude when working with agencies, and trusted them to innovate, and allowed for failures along the way (within reason of course) then I can see agencies driving more innovation. Unfortunately I don't see that shift happening.