If you do a search there's alot of threads on AIU. Kinda pricey, $28k for an MBA but you can also do it in 8mos which is a plus for some people. But perfectly legit and is Regionally Accredited. You didn't mention what program so I don't know what to tell you.
I am just about to start my third course with AIU so far I am pleased with them. I did have a few administrative hassles with them when I started, I needed to change my start date to commence with my actual graduation from my associate degree program and my advisor didn't want to change it. I was able to get a dean involved, the date was changed, and I've been happy ever since. The pace is a bit fast but I've grown to like it...the fast pace seems to keep me from procrastinating as much as I might otherwise have done. It's also nice that if you get a class you don't particularly enjoy it's over before you really start to loath it If you have any specific questions just let me know and I'll do my best to answer.