Yes it is, but only for your phone.
You can frie your processor, or not =)
Depends on how you do it, and depends on your phone too.
See my case, i never had a problem with overclock (not mentioning crashes and freezes, but it doesnt happen everytime).
Newer Power Kernels are very stable and crashes decreased significantly (bit this is MY case).
Some phones never run well with overclock, other ones even stock...
My phone is overclocked almost since i have it (about 1,5 year ago) and today it´s better than ever, with CPU Speed and Battery tweaks.
By default, it starts with 805Mhz, but when i want more, is too easy to change to 1000Mhz for a while.
So, i say you can try overclock, but pay attention on the tutorials and read carefully. Make each procedure as it says. And at every different behavior you notice, let the community know.
But, it is YOUR resposability. Do if you want to.

=)