BrightStar,
Some of the buttons, like Google +1 simply cannot pass strict validation. I've looked this up before and the work-arounds suggested were extremely convoluted and not something I would bother attempting.
It's not like there's anyone out there giving cash prizes to sites that validate properly.
predpriemach - I had problems with Facebook Connect this morning myself- it looked like some sort of conflict with "Add This." But it appears to be working fine now- please re-try.
Since all javascript is served from facebook, google addthis, etc... we are at the mercy of their developers- sometimes bug make it out into the wild.