While there are countless Digg clones out there (Pligg, Newsvine and Reddit, to name a few), only a handful gain enough traction to stay on the radar. Mixx is one of them, and the company has released metrics today showing steady growth over its year-long existence. Mixx reports that it has increased its monthly unique visitors by seven times, growing from 400,000 to 4 million monthly uniques since May.

The social news aggregator claims the major differentiator between itself and Digg is the attention it gives to its user base. It says this focus on its users is why its seen such strong growth to date. Digg, however, still brings in over 22 million unique visitors a month.

Mixx’s user-focused features include the ability to better control user comments and leaderboard recognition for the site’s top contributors. With funding earlier this year and additional investment from the LA Times, Mixx has sought growth through partnerships with mainstream print publications, just as Digg and another competitor, Reddit, have done.

Yet Digg is still far and away the leader. Mixx, Reddit, both of which have had similar growth patterns are still well out of reach of Digg’s dominance, according to web site ranking engine Compete.

To exacerbate the issue of differentiation, many features that were unique to Mixx and Reddit, such as subgroups within the larger social news site, have now been picked up by Digg.

Given Digg’s recent round of funding for $28.7 million, it’s likely that Digg will continue to keep pace with new releases from competitors, including Reddit’s open source option. Most importantly, however, Digg still has a stronghold on its community, which has stuck by the site despite complaints about sporadic changes to the algorithm and tweaks to the comments and recommendation systems.