I love mine. The power is fantastic.
I got the BTO with 16GB RAM and the 2.6 GHz processor upgrade. I am a Java/iOS developer and sometimes do minor things in Photoshop. I can run Eclipse, XCode, Photoshop, Chrome with several tabs, a Windows instance in Parallels with Eclipse and Chrome running, and Spotify with no noticeable lag. The screen is absolutely stunning and great for long programming sessions. I often prefer to use my 15" retina display over my 25" external display just due to the text sharpness. Also if you are an iOS developer you can use the simulator for retina models in all their glory, without the annoying stretching you see on non-retina displays.
I originally was considering waiting for the 27" iMac but I'm so glad I went for the rMBP. It's an absolutely amazing machine. It's power, screen resolution, portability, weight, and battery life are all top of the line.