I'm typing this on the same laptop, but I'm so ready to jump ship to a new rMBP once they come out. The one USB-C port is survivable, but having two would make life so much easier (much less four, if it is as rumored.) I also have a 4k monitor...but the 30hz limit is extremely annoying so I don't use my MB with it (I'm aware of the USB driver tweaks, but I'd rather have my usb 3 speeds and general stability.) Also I have lately been hitting the limits of a non-fan cooled CPU and when it gets throttled it gets slow (doing large xcode project builds.) Hopefully just a few more weeks.
The MacBook is limited, but oh so very light and small. It makes me forget the limitations sometimes which is great. 4K via the Apple AV adapter is limited at HDMI HiRes 1080p @30Hz which is OK, but a total waste of a nice monitor like mine. The one port doesn't bother me at all (USB C > USB C, HDMI, USB w/ 4x USB hub), but I would like a better video output. Haven't bothered looking for solution because this situation was supposed to be temporary.
Really hope the new MBP is much lighter and smaller than the previous model, makes so much difference.