At some point, nearly every social media startup intends to make money. Tumblr has held off for quite some time, but now they are about to roll out their revenue model: ads. [caption id="" align="alignright" width="240" caption="tumblr blog (Photo credit: Zadi Diaz)"][/caption] Their model will have a starting point of $25,000 to be included in their “Tumblr Radar” and “Tumble Spotlight” sections. The Radar is visible on every users’ dashboard on the right sidebar. The dashboard is the starting point (and most commonly browsed portion) for members when they are logged in and promises 120…