Are you sure?
Sorry, that was the point. We could talk about opinions, sure. But all major search contenders do significant user research into how people will react to much less significant changes than Instant Search. This change had its but user-tested and dogfooded for quite some time.
an example: Steam, the game delivery system, takes longer to deliver and properly execute games than it takes to buy one from the store, install it and run it. but you get more value from steam so people sit through hours or nights/days worth of downloading to run its games.
Still, a competing product will win both over if it can get sub-100ms response time for all of their UI interactions. Buy and listen to a song? Imagine hearing it instantly after you click "buy & listen".
Google and others have studied the response time -vs- user stickiness issue extensively, and it's good stuff to read - users don't even know what they want.
Example (paraphrased) - the majority of users will say "I would rather see 20 results on the page than 10" - but actual A/B testing shows that the users shown only the 10 results (faster, less information to process) are overwhelmingly more likely to continue using the service.
What people think they want when asked is very often not what really happens in practice.
So if a search engine is giving you results you hate - response time is obviously meaningless - but otherwise, it's everything.
Even if you don't have competition, you leave the door wide open if requests take 5 seconds.
There's also indirect competition ... like a lot of people type the name of the service they want directly into Google's search box ... a practice which would stop if it took 5 seconds, because accessing your local bookmarks would be faster.
if google were far better than their competitors at providing what users want (relevant search results they don't have to dig through) they could take 5 seconds and it wouldn't matter. the added value of getting what you want on the first try at the top of the page would keep people using that product.
yes, 500ms can seem like an awful lot when you come from a world of 250ms. but if the results returned from the 500ms are significantly better, you bet your ass users will sit through double the time to get better, more reliable results.