I lost mine last summer on a bike shop ride...twice in one ride! I felt like such a moocher 'cause I didn't have ANY tubes, so I had to scam from other riders. They were really great about it, but I sure learned my lesson. Never ride without a spare or two!

By the way, BOTH flats were on the *@%! back tire! Oh well, gave me a chance to flirt with the helpful tire changing guys.