I use multiple daily and have definitely seen a productivity boost. If nothing else, it saves typing. But I'd argue they are in essence a better search engine - it answers "you don't know what you don't know" questions very well, providing a jumping off point when my conception of how to achieve something with code or tooling is vague.
Typing is, or at least it should be, the least of your time spent during the day doing programming. I don't find optimizing the 5-10% of my workday spent typing impressive, or even worth mentioning.
Granted there are languages where typing takes much more time, like Java and C# but... eh. They are quite overdue for finding better syntax anyway! :)
I didn't mean typing in the sense of autocomplete, I meant typing in the sense of stubbing out an entire class or series of test cases. It gives me scaffolding to work with which I can take and run with.
