I can't speak to the Graphic Design program in particular, but I have been very happy with my studies at Penn Foster College. The courses are challenging, and although I haven't graduated from PFC I was able to change careers and get a new job just because I was enrolled and studying in a degree program with them.
I work with many graphic designers, and most of them either went to community college or took graphic design in a four year college program. To me, it looks like many of the courses at PFC are similar. As long as you have a good portfolio of work to show perspective employers, you can get a job in graphic design. A portfolio which shows what you are capable of doing is most important.