Have you been getting a flurry in LinkedIn invitations in the past few months? I have been receiving a few requests a week, so I wasn’t surprised to find that the market share of US visits to LinkedIn was up 323% in the past year (week ending 7/7/07 vs week ending 7/8/06), and up 17% in the past four weeks alone (week ending 7/7/07 vs week ending 6/8/07). As of last week, LinkedIn ranked at #23 in the Hitwise Employment and Training category.

What did surprise me in looking at the upstream data for LinkedIn was that Gmail figured more prominently than usual. As of last week, Yahoo Mail leads over Gmail in market share of total US visits by more than 10 to 1, but Linked In receives only 3X more upstream traffic from Yahoo! Mail as Gmail. This relationship can be seen by examining these two charts side by side. Hotmail is also less represented among Linked In users than normal. 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.