Valleywag

"But we prefer a simpler interpretation: Ebay has more money, from its outrageous monopoly on online collectibles and other auctions, than sense."

You are correct.

Here's my explanation for the acquisition: Internet advertising is where the money is, and StumbleUpon (it's a single InterCap company name) has stumbled right into the middle of the advertising business.

We spend as much on StumbleUpon "advertising," in which your site is inserted into the stream of recommended sites presented to StumbleUpon toolbar users, as we do on Google AdWords.

AdWords suffers from click fraud. StumbleUpon doesn't. And AdWords these days are costing $0.08 to $0.20 per click in our field. StumbleUpon visitors only cost us $0.05 each.

StumbleUpon visits have become a major source of traffic for us, and visitors from StumbleUpon tend to be more engaged, sending e-mail, asking questions. The context in which your "advertisement" is presented to them is more subtle, less advertisey than AdSense, almost like when a user of del.icio.us finds a link to a cool site on del.icio.us.

StumbleUpon's advertising offerings are extremely basic at this point, but very appealing to advertisers. Rather than attack Google on Google's terms, as Yahoo is doing with Yahoo Publisher Network, eBay may be doing a end run.

What artG just said.

It continues to suprise me that people are so clueless to the fact that end users hate advertising but eat it up if its presented in the right context. And that context isnt the sell its the the context of human self interest....

So yeah, Ebay is making the right move, and if they can scale it fast they'll make Google look silly for missing the opprotunity.