I do my own starting off with powerpoint or MS Word then print out on good quality card. I do not laminate in case people like to put them in a frame behind glass. The only handwriting on my certificates is my signature.
My skills in calligraphy have been left behind in school days - wouldn't trust myself to have the same quality of penmanship throughout the entire document without any errors or splodges. I admire those who can do it though.
