SlideShare, a company that lets you upload Powerpoint presentations to the web then share them with others, has raised $3 million from Venrock. Its site has been growing increasingly fast since it launched in 2006, chief executive Rashmi Sinhahmi tells me. It now gets 4.5 million unique visitors per month, with more than 400,000 registered users that have uploaded around 300,000 presentations to date.

The site lets you do things that you’d expect from this type of social software, like vote on your favorite presentations, see lists of the most highly-voted presentations, as well as embed presentations as widgets on other web sites. It is notably now large enough that its own user base is sending back substantial online traffic to people who post presentations, according to one of its angel investors, Dave McClure.

The company competes somewhere between document-sharing sites like Scribd and Docstoc and general online presentation services like Google Presentations.

The funding will be used to build out its team, its technology, and to launch more ways of accessing content topics on the site.

For more on the company, see the embedded SlideShare presentation starring McClure, above.

Besides Venrock, investors include Mavericks owner Mark Cuban, Friendster founder Jonathan Abrams, Google employee Hal Varian, Index Partners partner Saul Klein, and entrepreneur-investors Yee Lee and Ariel Poler.

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