I tried with a 15" rMBP but after 6 months I bought an 27" iMac. Sure I could just buy a Cinema display, but I found that to be cumbersome, having to plug the laptop in all the time. Especially the resolution change when going from "mobile" mode to desktop with the monitor connected, would bother me a lot. Windows do not keep their position and lots of resizing would have to be done..
Another factor to consider is that a laptop needs to be configured with energy saving in mind. So, I had lots of programs that I would normally configure to start with the OS, configured them not to start...Also think about Safari plug ins that you would normally disable when mobile just to save some energy but would like to use when connected to power..
Another issue for me is having to connect my external drives to my Macbook all the time. Sure, someone could use a NAS or a Time Capsule (which I also have), but the overall speed cannot be compared to Thunderbolt or USB 3...
Overall, the compromise was big for me, so I ended up selling the 15" rMBP and getting a 27" iMac. Much better for me!
I also got a 13" rMBP to use as a laptop...
Generally I believe computers should be used for what they were actually made for. A laptop is a laptop, and it will always have its limitations..