I will not save ~$50 to risk killing my camera... on the other hand, there are people who don't mind paying more for extended warranty which I find it useless...
It's all about perspective.
If one is doing it recklessly, such as buying 3rd party battery without checking on spec, etc then perhaps it is not worth the money saved. However, what Daniel has done has dispelled the doubts and I have no problems using the 3rd party battery on my OMD. I have been using 3rd party batteries on my E-P1, EPL1, EPL2, GH2 and now OMD for the past years, I have zero problems with them. Look before you buy and know the risks.
As for extended warranty, some people keep their camera for a long time so it make sense for them to buy. You find it useless but it is a great addition to others.