I am new here so take my thoughts with a grain of salt really but it keeps striking me that the 'texture' of each continent is the same. I figure its all the same bump map so this is not supriseing but it keeps makeing me think 'when I do a map like this, different bumpmaps for each continent...' Just a thought really. You could go back make a mask for each one and then bump them up or down or something to give it a less uniform feel. This is just my personal thoughts on it though and as I said I am new to all of this mapping stuff.