care to see if someone already wrote such an extension for smf? i doubt it but here is where to look:http://custom.simplemachines.org/mods/
1) it shouldn't disrupt the working of the page if user has js disabled
2) people on the forum have to agree that it's not a privacy invasion. i think as long as all it does it count clicks and doesnt save any other info about the user it's probably not going to bother anyone.