adding to bob's answer.
considering the current life span of mobile electronics I really wouldn't worry!
Yes, the processor on it, instead of lasting 25 years before burn n die will last only 23 years.. so don't worry!
Battery wise as well, instead of giving you 4 years of good life than an extra 2 of crappy life, it will be 3 years of good life!
remember.. ALL THOSE NUMBERS I said are purely guessing and have no scientific base!! They are for illustration purposes only.
fact is: in 3 years time you'll already have bought a n-videa core 8 based device that the screen is as thin as a piece of 300grm paper.
so conclusion: I wouldn't worry and enjoy the benefits of overclocking. But it's your decision!