Can I say a bit more about criticism on the side? I've learned to embrace it as a necessary step to self-improvement.
My formative experience as a PhD student was when a senior colleague attacked my work. That was after I asked for his feedback for a paper I was writing where I showed that my system beat his system. He didn't deal with it well, sent me a furiously critical response (with obvious misunderstandings of my work) and then proceeded to tell my PhD advisor and everyone else in a conference we were attending that my work is premature and shouldn't be submitted. My advisor, trusting his ex-student (him) more than his brand new one (me), agreed and suggested I should sit on the paper a bit longer.
Later on the same colleague attacked my system again, but this time he gave me a concrete reason why: he gave me an example of a task that my system could not complete (learn a recursive logic program to return the last element in a list from a single example that is not an example of the base-case of the recursion; it's a lot harder than it may sound).
Now, I had been able to dismiss the earlier criticism as sour grapes, but this one I couldn't get over because my system really couldn't deal with it. So I tried to figure out why- where was the error I was making in my theories? Because my theoretical results said that my system should be able to learn that. Long story short, I did figure it out and I got that example to work, plus a bunch of other hard tests that people had thrown at me in the meanwhile. So I improved.
I still think my colleague's behaviour was immature and not becoming of a senior academic- attacking a PhD student because she did what you 've always done, beat your own system, is childish. In my current post-doc I just published a paper with one of our PhD students where we report his system trouncing mine (in speed; still some meat on those old bones otherwise). I think criticism is a good thing overall, if you can learn to use it to improve your work. It doesn't mean that you'll learn to like it, or that you'll be best friends with the person criticising you, it doesn't even mean that they're not out to get you; they probably are... but if the criticism is pointing out a real weakness you have, you can still use it to your advantage no matter what.