Prior to the RVSM era, I flew an MD80 manually from Alicante to Stockholm at FL370 due AP failure. No issue really, except me and the Captain took turns in cruise to fly in order to let the other one eat and monitor a bit. My first airline gig was flying a regional turboprop in the U.S. without any AP/AT in all weather ops in congested airspace, so it felt as no big deal really..
I must be getting old, as I feel these days there is almost a sense of panic among the magenta generation if the AP is not engaged shortly after departure and kept on until fully configured/ trimmed out on short final....