If someone has given me rep for a post (e.g. my earlier post in this topic) then I can see the thumbs up/down icon beside the post number. Clicking this displays a popup (a nice HTML box) with the message that was received.

I can also see the thumbs up/down icon beside the post number of my posts within any topic that I've started. But clicking this displays a JavaScript alert box saying "This post has not received any reputation. You currently have 20 reputation point(s)."

I cannot see the thumbs up/down icon beside anyone else's posts.

EDIT: This very post has the thumbs up/down icon but displays the JavaScript alert box.