downloading abandoned software is just as illegal as making copies from a book you can only find at the library. ofcourse you are not hurting the sales of that specific product but it would prevent you from potentially buying new commercially available products. most abandonware sites deny this fact but the only reason they can still promote this view is because noone has bothered to close them down. it would be no problem to do so for any of the copyright owners whose software they distribute without permission.
ofcourse you also have REAL abandonware- but this is just another term for previously commercially available software that has been re-released as freeware. cheers to the companies who respect their loyal customers enough to choose this solution!
and fuck those who don't- that's what we've got warez for! :-)