Couple months ago. Removed all the keycaps, went through the entire thing with a vacuum and a fist full of cotton swabs. For the most part it's just dust and hair, since I don't eat messy food at the computer.
The old one I cleaned just yesterday actually, stripped it and cleaned it to the best of my ability. Surprisingly clean.
The new keyboard I'll probably clean in a month or so, it's still immaculate.
The switch from reds to blues literally jumped me 20 wpm average from day one. That tactile actuation is fucking sexy.