I second that Mark is due some waddage. Its worth remembering that the bolts in the quarries have never been in such a good state, and that slate is always a soft touch until you fall off...
A Few stories from my experiences rebolting.
Poetry pink, while replacing bolts the old post crux bolt sheered off with less pressure than opening a Jam jar.
Ditto the pre crux bolt on See you Bruce (my first E3 back when it was bolted more like an E4)
Rebolting the obscure Crook route, the Reclining Bloon I experienced the Home made nick walton bolt, a coil of sheet metal around a bolt that wiggled out by hand.
Going to rebolt the ILLJ route at the watford gap Suspension of disbelief, only to discover that every bolt was in a detached sheet only 10cm thick.
The Burning at Looning the tube, a rare over hanging route where every sling I threaded through the old hangers ripped through and I had to bolt off sky hooks.
The Vast majority of rebolts were done with 12mm bolts and resins, and we haven't had any problems with these yet, so hopefully there's less to worry about than the bad old days.. Its some of the new wave lowgrade sport that breathed a lot of life back into the quarry that have been suffering, but the adventures out there are still definately adventures, and maybe a little safer too..