Personna Lab Blue (3). Was good for more, but I have sample tucks to get through. No point dwelling on known good blades when there are experiments to be had!
Feather (7). I'm sure it was good for a few more shaves but this is the longest I've pushed any blade. If I didn't have DE Blade ADD this would be my everyday blade. Now it's on to the highly regarded Wizamet. I just received a box with 250 of them and I'm looking forward to seeing how they perform.
Tossed my Derby Extra blade after 5 shaves. It was still smooth and sharp enough to cut my mustache hairs, the toughest part of my beard. This blade lot was purchased pre-2010, so I don't know how it would compare with more modern versions of the blade.