I've been thinking about this for a LONG time now - sort of wondering if its really worth it.
1 - certain one's can actually bend your frame, causing more damage than they're supposed to prevent.
2 - You can pick up a used GRP race fairing for less than the cost of the bungs - and if you crash, just patch it up again. Where'as if you use the bungs - there will ALWAYS still be some damage to the fairing in a crash anyway.
Sort of thinking that it spending money for the sake of it.
Having said that - I've fitted some crash bungs at the bottom of my fork legs, as the fork bottom's aren't as cheap to replace as a bit of fiber-glass - and the kit only cost about £20.