I just got back from a 225 mile ride today (a bit chilly, but the heated jacket and gloves made it nice) and noticed that I have cord showing through the Pirelli Diablo rear tire. I had that tire installed Nov 27, 2010 and got about 5700 miles on it. That is not very far off from the mileage that I got from the first Diablo (about 6100 miles).
Its a nice tire, but that is not enough mileage. I already have a Metzeler Feel Free in the garage that is going on next week. Hopefully it will last longer. I already have a Feel Free front tire (installed in Sept. 2011, and now has just over 2000 miles on it), and it seems to ride as well as the Diablo.
Tires have always been balanced, and pressure is monitored at least monthly (and rarely needed more air). Valve stems were replaced April 1, 2010 when the first Diablo set was installed.
I like to ride hard, but I'm not a racer. I'm hoping the Metzelar is a better fit. Just letting you all know my experience in hopes it can help someone out there.