Twitter had a distinct advantage in that non-users could still, er, use the site and read threads and replies without logging in. Personally I have known not to

Twitter had a distinct advantage in that non-users could still, er, use the site and read threads and replies without logging in. Personally I have known not to click on Facebook links for years, but I could still give an ad impression to Twitter now and again. Now I just avoid Twitter links all together.