Acceptance of health treatment claims that are not adequately supported by evidence. I dislike it when people sell ineffective and even harmful alternative health products to exploit the desperation of people with chronic illness.
I find this website a pretty reliable source of info. It seems to say doses over 100mg a day are ok. There is some info there on what sort of doses would be considered toxic. http://examine.com/supplements/Alpha-Lipoic Acid/
It's a shame that supplements are not regulated like drugs, because it's hard to be assured that the ingredients match the label and that they have been properly researched and tested. Luckily there don't seem to be major issues with this supplement, from what I can tell from the site above.
I've been taking 500mg ALA and 500mg Benfotiamine together as a precaution as well. I haven't seen any issues. I believe the doses that have been applied in trials are quite a bit higher.