Is A 15-Second Ad Every 3 Clips Fair?

What's the tolerance for ads before online videos? I kinda like the Office Pirates model of one 15-second ad before every third video. Obviously we'd all like to watch our videos without ads, but then we'd have to pay for them or the companies would go the route of

On the continuum, iFilm is probably the most aggressive and Google Video the most laid back about ads. Think that will change? I see us moving to a model somewhere between iFilm and Google… and 15-seconds every third video seems fair.