Glide approaches are a good idea to be practised often and can of course be considered a "normal" approach, just as dragging it in under power can also be called a "normal" approach. Both are appropriate in different situations. Shock cooling is a problem, but as said, you should be gradually bringing the power back when approaching the field and thus the engine should be cooled from its cruise temperature by the time you pull the power off for a glide approach- or even before you start a powered approach.
Im very surprised at Classic's comments regarding people doing glide approaches because they cant do power on approaches. Ive never heard that one before, by heard and seen the opposite many times. You need to be much more precise to fly a glide approach and it improves your flying skills. Anyone can power on in and then cut the throttle over the runway and you see some pretty awful examples of this!
Someone said that the most efficient way of flying a jet is to stay as high as possible for as long as possible, then glide down to land without having to put power on. This may be true in theory, but even if ATC would allow you to do it, is never done. The reason being is that jet engines are slow to respond particularly from idle and you need to be able to add power quickly incase of a go around- or hit by a gust etc. Thus most airline procedures have you being up at 40% power or so by 1000ft on the approach at the latest.