I always try to mix in the "bad" stuff with the good stuff. Criticism is great, but only getting criticism makes you feel like a complete failure. I think that encouragement is just as important as criticism. After all, I'm just trying to help, not to make things worse.
Devastus
Of course being diplomatic helps if you want to be taken seriously, but basically an honest opinion is what artists search (and if they don't, they should) for. Constructive criticisms are much better than suck-up 10s, not to even talk about unexplained 0s.
The lower score will always 'sting' a little bit, but it's the trial and error that makes you better.
SFaPiL2 (Updated )
Thanks. It's good to know I'm not the only one thinking that way.