The proof of work contact form on my web site has a difficulty adjustment. I can it the annoyance adjustment. Any time I start getting annoyed by the volume of messages I receive, I bump up the diffic...
It probably adjusts only one way, as getting little messages is less of a nuisance than the nuisance of adjusting the difficulty?
In general, people are better at taking note that they're annoyed than at realising that they aren't annoyed.
In general, people are better at taking note that they're annoyed than at realising that they aren't annoyed.