Whilst especially with things like the LSAT and UMAT it is unfair that those who have the money are able to buy better study material, I think it's unfair to download things from companies that work hard to produce material for these tests :/
Having said that, I often dl books for a preview, then buy them if I like them, and delete the downloaded file. I usually end up buying 80% of the books I download. Things like e-book stores make it easier for me to preview files, and buy them either from the e-book store itself, or from retailers. Usually I find it much more appealing to have a legit copy in front of me (ebook wise) as they're better formatted etc.
Though I understand where book 'pirates' are coming from regarding cost, I don't think it's a completely moral venture to download books illegally - it is essentially stealing.