I've tried and failed to watch 2001 all the way through four times. I got about an hour in the last time...and it will be the last time.
I've abandoned a few books over the years but Michael Chrichton's Prey I chucked with about 30 pages left. It started so well and then went downhill steadily til I was sick of it (scunnered, as we say round here).
I gave up on Bonfire of the Vanities, Middlemarch (though I have a friend who's a literature wiz who tells me I should go back to it so I will), every Shakepeare play I've tried except Romeo and Juliet, Catcher in the Rye, The Pale King, and I didn't finish Catch-22 the first three times I tried but then I did and I loved it.