I purchased a second license about a month after I upgraded to 5.x version. My setup is that I have BI running 24/7 on a dedicated "weather" computer in my home office. I also have two other computers in the office so, while I'm in close proximity to the weather computer, it's a pain to scootch in a chair over and the computer is in a corner, just not easy to sit there for a few moments. So my purchase was mainly a big "convenience" but very worth it for my purposes.
I like the additional copy since you basically are getting another full license. The familiarity of the screens, settings, etc., are all there. I didn't "add" any new cameras or existing cameras to my 2nd copy, I just use it to remote into the main BI that I have running on the weather computer, although I guess you could have a couple of cameras set up on the second copy, not sure why you'd want to do that but there may be a reason why some people might want that.
During my first two weeks of using the remote console I had several issues and worked directly with Ken to resolve them. The *only* minor issue (and I wouldn't let it stop you from buying it) is that occasionally when I have the cameras up on the remote screen, when I click on one camera to open it or edit properties, on a rare occasion BI "thinks" I'm clicking on another camera and opens that one. No biggie, I usually just have to re-click on that camera (in the gray bar area) and it usually works fine but I still plan on reporting that to Ken when I have time to do screen shots or video captures for him to aid in the details of the issue.
One more minor issue is that if you use the second copy on a lower CPU machine it will most likely slow down other things on that machine while running it, but since I only occasionally get into BI remote console that is not a big issue at all.
All in all I really am happy with the second copy and depending on your circumstances on why you want to buy it, I'd highly recommend it.