Yes of course, always. :-)
But there are better ways to telll someone that he can improve something then telling it in a forum where a lot of ppl view it and might get a wrong opinion about my work. I personally would never go to someones server topic and write things like "oh this is bad and this and that could be better" or whatever. This wouldnt look good to other ppl as I should have my main focus on my craft and not on others - what I defineteley have. And IF I would find something I would write it in a personal message, but thats a character question.