ficwriter1966 passed the word that there were no spoilers up tonight (Yay spoiler distant early warnings!), but I used the screen anyway to see what effect it had.
It blocked all but the top line of the ever-present station 'bug' (tarantula, more like) and all but a faint glow from the assorted dancing, bouncing, distracting crap the CW puts across the screen bottom to advertise other shows. As a result it was much easier to focus on the show. Only about an inch or so of actual picture was blocked, and I found it hardly noticeable, though with a new ep, that might have been annoying. On the whole, I call that a success.
Anyway, there was no crawl, and no spoilers tonight, so here's hoping the CW promo people developed concious thought, and won't inflict that on us ever again.
Having said that, I'm not going to disassemble my spoiler screen yet. Just in case. ;-P