Speaking 100% truth can give you an amazing sense of power but it has some downturns too. If you're not being honest about yourself, it means you fear judgment and/or consequence of judgment from other people. So its necessary to develop your power along with truth. While speaking truth about others who may not be powerful might hurt them, so speaking truth about others should be done with care and love induced and with lots of understanding to avoid them getting hurt.
I did a 30 day trial on being 100% honest. I wrote about the experience here
My Experiments with Truth !!! 
Let me know what you guys think?
Regards,
Dhaval