The market share of US visits to LinkedIn was up 323 percent in the past year (week ended 7/7/07 vs. week ended 7/8/06), and up 17 percent in the past four weeks alone (week ended 7/7/07 vs. week ended 6/8/07), according to Hitwise, writes MarketingCharts.

As of last week, LinkedIn ranked No. 23 in the Hitwise Employment and Training category, writes Hitwise's LeeAnn Prescott.

Interestingly, LinkedIn users are much more apt to be using Gmail than the online population as a whole, according to Hitwise.

As of last week, Yahoo Mail led Gmail in market share of total US visits by more than 10 to 1, but the amount of upstream traffic from Yahoo Mail that LinkedIn receives is just three times that of Gmail, according to Prescott.

That relationship can be seen by examining these two charts side by side:

"It appears that LinkedIn still has early adopter appeal, just as Gmail does, and is poised for even greater growth as the word gets out," concludes Prescott.