This blows me away. From this article:
ShareThis plans to announce Thursday that it's raised $15 million from Draper Fisher Jurvetson, Reservoir Venture Partners, RPM Ventures, and Blue Chip Venture in a second round of funding. Since it was founded in June 2005, the company has drawn a total of $21 million.
That's a total of $21M for the maker, so far, of a sharing widget and toolbar. That seems a bit crazy. They must have something really big planned. I can see the usefulness of the widget and that it results in valuable data - what people are interested and who they share it with. But building up enough users to reach critical mass and then justifying that huge round is going to be tough.