From a TechCrunch post reporting on earnings (I think):
The company’s growth numbers seem to back that up. LinkedIn added 13 million new members in the past quarter, bringing the total to 174 million members. It’s also seeing an average of 106 million unique visitors each month.
So, officially 174 “members.”
I think 13 million new members is still over 1 signup per second… I’m guessing the signups per second has been decreasing… as it’s become more saturated in certain countries…