In reply to Wise:
People generally don't glue stuff unless its absolutely crucial for the existence of the route. Why bother if you can still do the moves without a certain hold? It's a lot of time and expense and most people would rather go climbing.
The most famous glued on hold is probably the one in Tom's Roof at Stoney Middleton. All the problems use this one finger edge in the middle of the horizontal roof. I think it was Tom Proctor who glued back the block that the edge was on more than thirty years ago. The glue used is Araldite and given the fact that some of the problems involve cutting loose with both hands on the finger edge its pretty damn good advert for the efficacy of Araldite.
These days though Araldite is too expensive for gluing bits of rock and most people use cement, typically the same stuff they use to cement in bolts. In France cement by the brand name Sika is commonly used and a verb 'to sika' has evolved to describe such work.