Hi there shappil,
Welcome to the Forum.
As far as I know, there is a small community of people in Taiwan who regularly write Taiwanese in POJ. Those people seem to know quite well the tone-numbers and diacritics to use. The basic core of these people are probably Christian-based, or the descendents of people who are Christian. If I understand correctly, they publish newsletters and that sort of stuff in POJ too. (Though this is probably not on a very large scale.)
If I understand correctly, there are also some non-Christian Taiwanese who also use POJ on a regular basis (though this would probably be a much smaller group even).
A small sub-group of the above community (or just "group" or "these people", if you prefer) are probably the ones who update and add to the POJ-wikipedia:
http://zh-min-nan.wikipedia.org/wiki/B% ... 2m-g%C3%BA.
Outside of this group, I know of almost no one who knows and writes tones for Hokkien. In Malaysia and Singapore, they are not even aware of the b-/p-/ph- and g-/k-/kh- distinction, and tend to write POJ p-/ph- and k-/kh- as b-/p- and g-/k-, based on their knowledge of pinyin. It always frustrates me to see Hokkien being written like this (I've said so in other postings on this Forum). I mean, I don't mind if people *REALLY* know what's happening, and use bb- and gg- for POJ b- and g- respectively, but a lot of the Malaysians and Singaporeans who write Hokkien "informally" DON'T know this, and simply ignore the distinction between POJ p- and b- (and between POJ k- and g-), probably writing both as just b- (respectively g-). This I find very sad.
In my experience, these people never write (or even know) tone-numbers. They write toneless pinyin adapted for Hokkien, and hope that the user works out which words they mean from context. [BTW, I don't view the omission of writing tones too negatively. I often do it myself, because: 1) writing a tone on every single syllable is a lot of extra work (and it
can very often be worked out from context), 2) working out the tone is quite tedious, especially as the majority of syllables are pronounced with sandhi-tone, so it takes even longer work out what the citation tone is, in order to write it, 3) writing tones as numbers looks pretty awful (IMHO), 4) writing tones as diacritics looks a lot nicer (again, IMHO), but takes even more effort.]
So - to summarize - outside of the Taiwanese POJ-users, I think very few people (particularly in Malaysia and Singapore) know much about Hokkien tones. The exception being the dedicated contributors to this Forum, of course.