Yep, I agree with nomanstool. I've just purchased the rMBP to use as well as my iMac, as they are integral to my work and I need the flexibility.
I will use my iMac more, as its set up in the office and is more powerful, even if it is slightly older.
But I need to be able to take work home with me, which is where the macbook comes in. I struggle with laptops if I have to use them over long periods of times, so I see it very much as a secondary / casual use computer, but need the spec of the macbook pro for the programmes that i use.