I add my contribution to this thread by saying that I also recently discovered Collectorz and it's bringing me back to the comic books world. I have been an avid comic book reader for my entire life, but I stopped buying and collecting some years ago. I was tired of all the relaunches, the new titles, etc. It was difficult to keep track of everything.
Collectorz makes it so easy to add comics and follow a series! I have scanned all my comics in few minutes using their iPhone app, and now I am having fun going through my collection with the web-based software, and I can finally see any gap