It's not so-much an advertisement inside of an advertisement - rather, the right way to think of it is like the new Facebook formats: an advertisement that allows viewers to engage directly within the unit.
While watching ESPN this morning, a commercial aired for a new show on the Golf Channel. The unique part was that the 'footer' of the screen had a large option for viewers to 'opt-in' to automatically record the show via the DVR.
This is the television equivalent to "becoming a fan" on Facebook: by opting in, I effectively begin a relationship with the Golf Channel, who is willing to pay a steep premium for that sort of engagement and data to Comcast. Rather than buying demographic based eyeballs, the Golf Channel will understand true conversions, viewership funnels and all within a data-driven / predictable model.
... And as a consumer, I loved it. Anytime the advertiser, consumer and middle layer all win, it's a success.