I've downloaded two sets of brushes from here (made by Brooke: Paint Stroke Brushes and Grunge Paint Brushes) and the .abr files won't load. I am using Photoshop CS2. I thought I remembered reading something recently about how newer versions of PS let you make brushes larger than 2500x2500 pixels, so I was thinking maybe that's the problem, that perhaps these brushes are larger than my PS will allow. CS2 and below, at least, do not allow brushes larger than 2500 pixels. I tried googling for info to see if that is the case (about the newer versions letting you make bigger brushes) but nothing came up, so perhaps I misremembered. Any other thoughts about why these .abr files might not load? With the first set I just used the pngs to make my own brushes, but I just download one with a *lot* of brushes, which I wouldn't have done if I'd known I was going to have to make each one individually from pngs.
If the issue is indeed about the brush size/version of photoshop, perhaps you could add a note to the item descriptions saying ".ABR only works in CS_ and above."