The pop-up window has grown in usefulness since the forums came back up, and I though of another use. On the bottom of the window, there could be a snippet of the most recent post. I like to look at what posts some people have made, but I don't like having to go to the main member page and look at the posts tab. It would be easier to have a preview in the pop-up member window.
To be honest, while there are a select few, including yourself, that would benefit from seeing a member's most recent post, most users are not very interested in seeing another member's posts. However, if they do want to view someone else's posts, they use the posts snippet in the user's profile. I know that it may take a few more clicks, but most people don't get bothered by that. I honestly doubt people even use the post snippet in the profiles very often anymore.