After 4500 miles since late March on the new Defy 1, I popped a nipple today, a spoke nipple. I was in the last 4 or 5 miles of my 40 mile ride when I hear a spoing. Stopped and I found one of the spokes was loose on the rear wheel--it was around 06:40. I biked the rest of the way home, got the cycle up on the stand and removed the rear wheel. I noticed the nipple was missing. Anyway, I took it to my LBS when it opened, told they'd do it right then, and replaced the nipple(the old one seemed to have just come unthreaded, but the mechanic put a new one on). He checked the wheel for being true and made a few adjustments. The charged me only $10(normally it's $20 but I bought the bike from them) and I was out the door in less then 10 or so minutes.
Had this not happened, I was thinking of doing 50 miles or a metric century, but I didn't want to do that many more miles with a loose spoke.