I genuinely wonder this. Can I say, "it's OK for XYZ to scrape, but not ABC?" (Or is it general use -- scraping OK/not OK?)
I think it's different for API usage, because you enter an agreement with an entity by signing up, etc. I'm speaking specifically to the unauthenticated scraping/indexing.
That said, once I've given it to you, if you choose to give it to someone else, I have no claim against that someone (although I might against you, depending on our contract). That's the heart of 3taps' position as I understand it; they get craigslist post data from third party sources like search engines, instead of scraping craigslist, and so do not have a contract with craigslist.
What about "anonymous" scraping, however? (I put it in quotes because I know you can reverse DNS/UserAgent/etc. identify... but that's simple to spoof, and we're discussing within a sophisticated context.)
Can I say that "OOgle" can use my data (because I want visitors) but others can't? (To complicate, can I exclude only certain, specified, parties and include all others?)