So does anyone else have this problem? As you ride a couple of miles, your seatpost starts to sink lower into the seat tube? I've tried tightening the bolt as much as it can go, and I've ended up stripping off the nut a few times (I now carry spares in case such a thing happens during a ride), but nothing seems to hold the seat in place over a period of 10 miles or so. It's especially noticeable if I unexpectedly hit a bump and wasn't prepared for it, so most of my weight is on the saddle.
Any suggestions? Besides "lose more weight", that is