I would like to be able to see which users are on my list, too... not just on the search results, but also on the transfers. I like to browse my downloaders' files and see if I want to add them to my list based on what they're sharing. I can't tell if they're already in my list, though, except by right-clicking on them to see if it says "Add user to list" or "Remove user from list". It would save me time if I could just see who's already on my list.
Bold text seems like the easiest option. Other options are a different color, different icon, or an extra indicator like a dot.