Roller lifters have a definite advantage,especially as Henry pointed out with zinc being removed from oil,flat tappet cams are certainly at a disadvantage as far as accelerated wear is concerned.But roller lifters are not perfect either,I can tell you from my own experience at having a lifter explode and ruin a cam.What happens is that after time,especially if you are using high lift cams and heavy duty springs,the needle bearings in the lifters become flattened,or knife edged,because only one side of the needle bearings take a beating at a time,then there is more and more play in the lifter wheel and eventually they will break.When that happens,peices go flying everwhere.Joe Schubeck at schubeckracing.com has interesting theories on this matter.He also produces roller lifters that do not use needle bearings,they float on a film of oil much like crank and rod mains do,but they are expensive.Most cam companies also manufacture a higher end lifter that is supposed to supply more oil to the roller wheel/cam lobe area,but they still use needle bearings.Also, mods that work with flat tappet cams do not necessarily work with rollers.Thrust washers and cam buttons are needed.Windage trays and crank scrapers are not recommended,and oil restrictors are not a good idea either.Roller lifter oiling is mostly acheived from crank windage,this is very important!But let me also say that my first solid roller cam had been in this motor long before I bought it,I'm guessing at 15 years,lots of abuse and hard driving,and if I had of known at the time what that squealing noise really was,instead of tightening the alt/power steering belts I could have replaced the lifters and still be using that cam!