Privacy/Security

Convenience

Ease/Functionality

The Three Musts

Privacy and Security Issues

​Delicious: A Cautionary Tale

Keep in Mind: 
Social sharing data is important - it gives metrics for time, eyeballs...and money. See this 2015 blog post from Shareaholic about their data: In Q4, Social Media Drove 31.24% of Overall Traffice to Sites [Report]. What you share is noted in the aggregate, and via tracking tools, in the specific (Note, this is based on Shareaholic data only, and there are other similar tools). 

2017 data (more reports - nothing newer)