I've never taken it but I do know that there are a lot of credit card scams out there using a free sample of Acai berries as a tempter. You pay postage with your credit card, so be careful if you buy online.
I use Acai juice in my morning smoothie sometimes. It is not cheap, so I do not use it often. I think because I only use about 4 oz's at a time I never noticed a difference on days when I use another juice. The main reason why I started using it though is because of Alton Brown.
I have been curious about acai, is it good for anything in particular or does it fall into the antioxident rich category? I have been seening more juices that have this as an ingredient.