Having been so happy to see the user defined python functions in QGIS to get the user name and scale in a label I thought I'd have a go at getting the coords of the map center into a label.
After quite a bit of playing around I've managed to get something working!https://gist.github.com/mtravis/e7aee748a4779996aa42
It gets the x,y coords of the current map canvas and then turns the x and y into a whole number and then a string. The raw function gave too many trailing decimal places for my liking.
It automatically updates when you move the map around too! If you move the map content in the composer window you will have to click the view extent in map canvas button in the item properties before seeing any changes.
As we have a few user defined functions now I was thinking of adding them to our github site. If you have any others please share them here and I'll add them to.