To what extent have the Psalms, Torah, Prophets and Gospel been corrupted?

I understand that Islam holds the previous revelation from God to mankind in high esteem, and that the "Psalms, Torah, Prophets and Gospel" are considered to be authentic. Nevertheless there also seems to be this view that all these previous revelations have been corrupted. My essential question is: to what extent? Is it considered profitable to pick up a bible and read the Psalms, Prophets, Torah and Gospel, despite their being corrupted? Or are they considered to be so far gone that there's no point reading them because what you would be reading is so corrupted that it's nothing like the original revelation? Is there any value in reading the Torah, Psalms, Prophets, and Gospel today? To what extent have they been corrupted?