eBay's most famous acquisition is arguably Internet telephony service Skype, which it purchased in 2005.
"StumbleUpon is a great fit within our goal of pioneering new communities based on commerce and sustained by trust," eBay's senior director Michael Buhr said in a statement. "StumbleUpon's downloadable toolbar provides an engaging and unique experience to its users, but it is the similarities in our approaches to the concept of community that make it such a compelling addition to eBay."
At last count, StumbleUpon had about 2.3 million members, and buzz about the site had spread largely by word of mouth.
The $75 million price tag is more than previously expected. Earlier this month, when eBay was reported to be in "advanced talks" to acquire StumbleUpon, the numbers being tossed around were about $45 million. Rumors about an eBay-StumbleUpon deal first began to circulate in early April.
It was a day heavy with acquisition announcements. Also on Wednesday, CBS announced a $280 million purchase of music social network Last.fm, and Fox Interactive Media confirmed its long-rumored acquisition of image-sharing site Photobucket.