Well I have ridden with the rubber doorstop a few days and it ROCKS!

Seatpost boinging aside, the suspension ceases to be an issue. There is sufficient spring to soften the edge off bumps, and enough damping so you don't bounce in the saddle. It feels exactly like the tyres are pumped soft.

I very strongly recommend this upgrade. I have written a simple procedure for doing the replacement, but pictures are still to be taken. I will place the procedure and edit it once I have the pictures.