A copyright lawsuit? Remember that a search engine ultimately functions at the sufferance of copyright owners. If push comes to shove, the engine is obligated to stop storing and serving data they do not own.
When Google was ascendant, the threat of a delist was enough to cow copyright owners into submission (see: news orgs vs Google News, Belgium vs Google, etc). Now, well, who knows?
That said I think this is a greedy and dangerous move on Microsoft's part, and I'm sure this is what Murdoch was alluding to a couple of weeks ago. This could kill the spirit of 'net neutrality for good if they simply move the battle to different layer of the stack.
On the other hand, I like writing metasearchers, so it might be a net win for me. :)
Are you sure that indexing is a copyright violation? You aren't reproducing the text in full and it seems like excerpts would be part of fair use. Do you have a source?
Parker v Yahoo takes the view that putting content online is implicitly allowing indexing. By the same logic, explicitly blocking an engine would mean the opposite.
The first link is about scanning, storing, and making available entire books. The last is about the caching ability.
The second one includes some great information, but if you read about the specific cases (starting on page 6) you can see it is still very much up for debate. Actually it seems that the courts have ruled in Google's favor almost every time, and most of these are for caching and not indexing.
You are right that search engines have made some advances in the courts in recent years, but the bases for their wins are thin and not the same in all countries. Barring legal action a site can block Google's known IPs entirely, forcing a search engine to either give up or use subterfuges that are probably not practical for a large public company to use.
If a site really really wants to block a particular engine run by a for-profit company, or make it impractical (either legally or technically) they can.
