> Whilst it may be asynchronous, people do have an expectation of a reply within a reasonable time frame - hours to a few days depending on the relationship.
Not at all, unless frequent contacts are expected in which case you should be warned through other channels.
> You end up wasting time waiting for a repsonse when you culd have immediately sought assistance from an alternative contact.
If you need fast turnaround, use a fast turnaround transport. That's what instant messengers or phones are for.
> It's not spam. It's polite and helpful.
I completely disagree, especially when the numbskull using out-of-office replies can't be arsed to turn it off for mailing lists. It's spammy, impolite and unhelpful.