Not only did my 0.5mm hot end block completely, but using too much force whilst it was mounted broke a Z-axis coupling! By luck I had printed a spare just a day earlier.
[ Edit 27.4.11: I should clarify - I was putting too much pressure on the entire x carriage as I was trying to push through some blocked filament by hand ]
Why doesn't the prusa just attach the motors from beneath with a gear like how the old mendel does it? Whats the benefit? This coupling broke, I dont see it as reliable.
I had a similar problem. I managed to break a Z coupler. I manageg a quick bodge repair witha cigarette lighter. Heating both faces and applying them together got me going again. Obviously my next print was two spare z couplers. They are still spare, my bodge repair is still holding out.......