The permalink for the vote is just pointing to the post, using the get_permalink() function, then simply adding a "add=want&id=postid" query string to the end, which is picked up when the link is clicked. If this link is pointing somewhere wrong I advise that you check the permalink settings on your WordPress installation, and check that "get_permalink()" will return the correct link to the post.
Ah, regarding the use in a visual editor - that is an oversight, as this is the very first release - it was something that was overlooked, I may look into having a tick box on the New/Edit posts screen instead.
It would be a great idea to have different designs, and this is something I will be looking to implement shortly, again - with this being a first release I just want to check that all coding is correct, and people can install without any issues before developing the code any further.
AJAX is a great idea, again this will be included in upcoming versions.
Thanks for your feedback, it's greatly appreciated.