Really great Kev. I particularly like the way you can use one block to shove others around!
The only thing I found confusing was the rotate functionality - whenever I press the RMB while holding a block in mid-air via the LMB, the block drops away. The only time I could rotate a block was when it was already resting on a surface - and then it wouldn't rotate freely due to the interference from the underlying surface.

KEV: Hold both together - LMB & RMB - though I'll change it to just holding right button I guess :)