It looks like perpetually almost-for-sale social news site Digg is going to stay solo for awhile… The SF-based company has just announced a big, $28.7 million third round led by Highland Capital Partners. The company has now raised $40 million, having last raised $8.5 million in late 2006. The current round includes past backers Greylock Partners, Omidyar Network and SVB Capital. So what can a user-gen site, which functions by letting users submit and vote on links, do with so much cash? The company says it will double its staff, from 75 to 150, expand into other languages, move to bigger San Francisco digs, do more marketing and build out publisher analytics tools (think: another revenue stream). With the announcement, Digg says it’s ad revenue has tripled over the last 12 months, though there are no numbers given out, and it’s not clear how much, or if, they’re making money on that revenue. Either way, they must’ve been able to convince their investors of meaningful strength to pull down a raise of this size in this market.

SEE ALSO: Digging on Digg: Early Days on A Deal

The canned quote from founder Kevin Rose: “We started Digg in 2004 based on the concept of using a collaborative filter of a larger community to prioritize the overwhelming amount of material online. While the growth of Digg has been phenomenal, Digg today still represents a fraction of our vision for where we can take this concept. This expansion and funding will help us get there faster.”

Read more in the release and in this blog entry from CEO Jay Adelson.