How viable are ad rep networks in 2011? (Gorilla Nation, Media Mayhem, etc.)

Do those of you who sell (or used to sell) CPM inventory through advertising brokers, such as Gorilla Nation or Media Mayhem or similar, find that method of monetization as effective as it once was?

If you don’t find that viable any more, what have you replaced it with or added to it? CPC networks, in-house ad sales, affiliate upsells, or ?