I do it myself every couple of months. I try to stay towards a lighter shade since when I go darker the gray shows up better and sooner.
every so often I get the nerve up to highlight my hair myself too.
I have had my hair professionally colored once and I liked it and it lasted a little longer than when i did it but I cant justify spending that much money on myself,and have had it pro highlighted once and again, it was expensive and didnt look any diffrent than when i do it myself so I will never pay to have it done again.