As I said in my first post, I'm interested in your personal use-case. I'm interested in hearing whatever works for you. Only you can answer how you use your devices and which are the right tools.
The reason I ask is simple. My needs are beginning to change and I'm thinking I don't really need both an iMac and a 13" rMBP as one of them is gathering dust. It is a luxury. Previously the iMac was my personal computer for media, movie-watching, SketchUp, personal files and data, whereas the rMBP was used only for school, brought to uni everyday. Now, my studies are coming to an end and I will hopefully start my career soon.
The reason I consider going iMac, iPad and iPhone is that I suspect a future employer would most likely supply a laptop. (Probably Windows, yuck). This would then be used only for work, while the iMac would remain my personal computer, like previously. Moreover it seems more fitting to keep personal files and information in a desktop at home, rather than in a laptop which is brought around. However the more I think of it, the less I find myself willing to give up the rMBP. I don't think the iPad can replace it, much like this thread suggests.
To all of you who have taken the time to respond, thank you. Keep it up, I find the replies very interesting.