Not sure but I think the "like" is a Facebook thing and it probably shows up on your Facebook feed. The "thanks" are a geckoforums thing and so they are tracked on the site.
No, my Facebook account isn't connected. Looked at the code and it doesn't seem like it'll do any unauthorized Facebook logging from the HTML that's been generated.
Oh, good. I like to keep different parts of my internet life separated. I agree though that it does seem kind of redundant, especially if it doesn't actually do anything on Facebook.
Maybe thanks is for when someone helps you with something. You know, when someone helps you with the care of your animals or whatever. And like is when you just want to like or agree with something they have said.