There is a strange disconnect between many of the experiences reported on this forum and my own.
After reading these forums, I expected it would be a tough tradeoff for me: lots of limitations vs. portability. But, when I finally got to the store (expecting to pick up a 13" rmbp), I was blown away by the rmbp, and bought it (they had the one I wanted in stock). It's been a week since I purchased it and I'm enjoying the computer immensely. I've encountered no lag and no pinwheels (beyond the expected ones I get on my 15" 2013 rmbp when Spotlight is indexing or I am doing something intensive).
Of course, everyone has their own expectations and use cases. I am a historian who primarily uses Office (Word, Excel, and Power Point), DEVONthink, Scrivener, Adobe Acrobat Pro (lots of scanning, PDF OCR, etc.), Safari, Thunderbird, etc. I do not play any games on it. Having a single port is no big deal for me, though more would be appreciated (Apple sells an expensive adaptor if you use projectors or need to plug in something while charging). If you have a similar use case to mine, I think you can expect that the computer will perform wonderfully.