It's a fun challenge, if often times difficult to learn and write a accent out without it being unreadable. I've tried afro-Carribean accents, African, German, and Boston accents. Most of the time - apart from German which is pretty easy is often stereotypical - it's a delicate dance of keeping up character, readability, and me simply keeping it up (the Afrocarribean and African accents I found to be the hardest).