It's only a small sample size and not against NBA talent but JLin is shooting 6-10 from the NBA 3 point line in the summer:
Las Vegas Summer League 2/3
Yao Charity Event 3/5
I don't think his 3 point shooting will be too much of an issue. Of course, he still needs to work on his form and range. However, I'll go out on the limb and predict his 3 point shooting percentage will be higher than Rajon Rondo and Derrick Rose this year.