At the moment, separate icon image files are loaded whenever any standalone services are chosen.
Performance can be improved by combining all of these icons into a css sprite. Whenever the admin adds/removes standalone services and hits Save, this should trigger the creation of a CSS sprite including icons for all the selected standalone services.
There are lots of free web services for creating sprites, and many of them offer APIs as well...
I understand that there are a couple of services for which sprites can't be used - Facebook Like, Google +1, etc. But the rest can and should be combined into a sprite.