All the social sharing buttons use 3rd-party JS. You can see the "embed" code for Google's new +1 button here: http://googlewebmastercentral.blogspot.com/2011/07/1-button-... This lets the sites update APIs without breaking every page on the Internet :)
And disabling all those crappy social sharing buttons makes the pages so much better. From faster loading to less clutter there are a bunch of benefits. Sometimes I'm flabbergasted how crappy sites are when I sit down to a machine without a javascript blocker.
