I think most people would be okay with this.
In my experience of using web forums over the past 15 years or so I've only ever had two people take offense at getting a random PM from me.
One of them was upset because I hadn't interacted with her on the open board yet and to her it was like a random stranger in a crowded public place just coming up and starting a personal conversation with her without even a formal introduction. The other--well, what I said to her was pretty tactless and I can see why she found it offensive.
Incidentally, both of them were British. I think possibly U.K. people put more stock in personal formal introductions than much of the rest of the world.
So unless it's someone with a rather extreme sense of manners and propriety and privacy (as ridiculous as it is to expect privacy on the world wide web, sheesh anyone can access the Internet you know) it is generally not considered rude to PM WP members without permission. Personally, I think it would look awkward to ask permission out here on the board. What would that look like? "Hi, KraftieKortie, I like your posts, would it be okay if I PM you?" erk.
Disclaimer: I am not nor do I claim to be an expert on nettiquette or any other form of communication etiquette. I am as much a socially awkward Aspie as anyone else on the Autism Spectrum.
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Your neurodiverse (Aspie) score: 141 of 200
Your neurotypical (non-autistic) score: 71 of 200
You are very likely neurodiverse (Aspie)
Official diagnosis: Austism Spectrum Disorder Level One, without learning disability, without speech/language delay; Requiring Support
Last edited by LyraLuthTinu on 20 Feb 2016, 5:58 pm, edited 1 time in total.