I (northern UK based) find "an user" feels wrong as to me the "y" implied by the way "u" is pronounced is a consonant sound so it should be "a user" - though I pronounce the "a" in a softish manner (more towards "ey"), it might be different if you pronounce "a" harder or pronounce the "u" as more towards "oo" (reducing the y-like mouth movements).
Regarding herb: in written word it is "a herb" for correctness, though few in the north pronounce it exactly that way as the "h" is dropped to produce "an 'erb" or sometimes (though this makes you sound uneducated due to certain stereotypes) more like "a nerb" (this time with the harder "a" as in "an".
It's nonsense like this that makes me pity you brave fellows who attempt to master our pidgin of a language!
The fairly arbitrary set of incompatible rules and standards that make up the English language mean it is difficult to learn perfectly (especially as there are arguments as to that "perfectly" means in this context) but it makes the language easy to learn to the point where you can survive using it in the languages native land(s) easier than many others. We are so used to subconsciously processing all the different accents we have in the relatively small area that is the UK and the extra nuances that creep in from elsewhere (poor education, influences from other cultures mainly via TV/film & music, etc.), that unless we are feeling pedantic we also naturally screen out the mistakes non-native speakers make.
It is common to respond to people apologising for their bad English with something along the lines of "don't worry, I deal with worse from people who have been here for generations". We are not being patronising here (well, at least some of us aren't!): sometimes we genuinely do have to internally correct/translate more when talking to someone from 300 miles away than we do when talking to a Pole/Spaniard/what-ever who is not (yet) particularly fluent in English.
For "hotel" and some others, I believe the difference is whether or not the "h" is aspirated. That is, whether or not you take a short break at the word boundary. If you say it "in one breath", you get "an-(h)otel" with a very soft h and no or very little aspiration.
If you make the word boundary more pronounced, you get "a hotel" with a clearly noticeable air-burst, and a clearly distinct "h".
Same process as with "herb" etc. and some other words that can be pronounced both with and without aspiration in English.
This is much the same as in French, where if the preceding word end in a vowel (with certain exceptions) and the current word starts with a vowel sound, you can usually elide the last vowel in the preceding words except when the "h" is aspirated. My French teacher liked to say that the French "thinks" they are pronouncing the "h" in those few cases (aspiration usually refers to cases where there's a strong burst of air in pronouncing the sound, but in French "aspirated h" does not actually involve fully pronouncing an "h", though there may be some aspiration)
(I may confuse this - this is based on recollection of my French classes 20 years ago...)
There is a scene in Hot Fuzz where the police have to take along an 'interpreter' so they can talk to a West Country farmer who is speaking English, but with an amazingly strong accent. This scene was apparently based on a real event they saw during their research for the film.
(I think it's 'west country'... I'm not quite up-to-speed on my UK regional dialects)
Regarding herb: in written word it is "a herb" for correctness, though few in the north pronounce it exactly that way as the "h" is dropped to produce "an 'erb" or sometimes (though this makes you sound uneducated due to certain stereotypes) more like "a nerb" (this time with the harder "a" as in "an".
The fairly arbitrary set of incompatible rules and standards that make up the English language mean it is difficult to learn perfectly (especially as there are arguments as to that "perfectly" means in this context) but it makes the language easy to learn to the point where you can survive using it in the languages native land(s) easier than many others. We are so used to subconsciously processing all the different accents we have in the relatively small area that is the UK and the extra nuances that creep in from elsewhere (poor education, influences from other cultures mainly via TV/film & music, etc.), that unless we are feeling pedantic we also naturally screen out the mistakes non-native speakers make.It is common to respond to people apologising for their bad English with something along the lines of "don't worry, I deal with worse from people who have been here for generations". We are not being patronising here (well, at least some of us aren't!): sometimes we genuinely do have to internally correct/translate more when talking to someone from 300 miles away than we do when talking to a Pole/Spaniard/what-ever who is not (yet) particularly fluent in English.