For years I used addthis services for social media buttons and am still satisfied with their great service, however there were few problems:
Difficult to modify Social media buttons
Addthis easily places social buttons on website, however I found it difficult to modify (float, fix the buttons) to sync with my website design.
More server calls and hence more pageload time
For every social media button, my webpages used to call Addthis and then later required media buttons like Facebook, G+ etc. Recently when facebook like buttons were having problems, the page was taking few minutes to load completely creating terrible user experience. I decided to switch to text only Social media buttons then.
Most users still copy URL and share
My Addthis analytic showed that 80% viewers copied url for sharing, perhaps because sharing buttons were at bottom of content. I placed those buttons way down for better user experience, as told before.
Social media buttons were bad for SEO
Not crazy about social media popularity count
I am not crazy how many shares/likes an article got. Any content which gets popular will drive more traffic for that page and I could always track its progress through Server log Analytic. Just check the page and referrer, this makes those count absolute numbers nothing much !