In normal conversation, I use "you".
If I'm trying to sound proverbial, then I might use "one". If I'm trying to sound biblical, I probably will use "thou". But in those cases it's usually more a case of being indirectly personal than being impersonal, and it's usually in fun. If I really care about something someone's done, though, I'll simply use "you" and have it be a personal expression.
I agree that the English language doesn't have enough words for "you" although it does have many colloquial plural "you"s like "y'all", "you guys" and "yous". I find myself needing to use a plural "you" much more often then I find myself in need of an impersonal you but I sometimes get annoyed by English's lack of an impersonal pronoun.
I'm kinda puzzled by the fact that there are "yous", "y'all" and the like but there is no colloquial, impersonal "you". I would imagine that it would be needed very often to clear up ambiguities.
Grammatically speaking, "you" is the plural second person pronoun already. English has merely morphed it into the singular first person pronoun as well. The true singular second person pronoun is "thou", not "you". So your problem stems from the fact that Anglophones use the 2nd person plural as the singular.
For comparison, consider French. Here are the relavant pronouns in each language:
2nd Person Singular
thou,
tu
2nd Person Plural
you,
vous
In French, you use
vous when you are talking to a group of people. With time (sometime around the Middle Ages)
vous also began being used as a term of respect to those with a higher social standing than you (or equal, depending on where you were to begin with). Nowadays, one would use
tu when talking with family, friends and children, and
vous with most adults, especially in formal situations or where they have higher rank than you (i.e. your boss).
Tu is also widely used amongst teenagers amongst themselves regardless of how well they know each other. To call someone of higher rank
tu can be an insult, and there is a verb (
tutoyer) for this action. On the other hand, as
tu is used amongst friends, it also can be a signifier of a more amiable relationship.
In English, by comparison, a similar thing began happening in the late Middle Ages, with
you being used around those of higher rank rather than
thou. In some Shakespeare one can notice
thou and
you differentiating rank, but even by Shakespeare's time
you was being used with those of lower rank as well at times. As time kept going on, English merely switched entirely to using
you in the singular rather than
thou. It's the same thing that happened to French, except taken to a higher degree. Nowadays many Anglophones consider "thou" to sound formal and stilted, when it actually is informal. This can pose a nice opportunity for a subtle knack at someone who doesn't understand the difference.
So the solution in English is to revert to using "thou" for the singular, and keeping "you" only for the plural, or formal if you prefer that as well. The only challenge is convincing the other billion English speakers to do the same

.
Of course, for impersonal expressions the French generally use
on, a third-person singular pronoun. It's pretty much a direct equivalent of the English
one. So those of us, myself included, who tend to use "you" in impersonal expressions, are just not using the right pronoun at all. I only used "one" here because I was thinking about it - in every case "one" appears in an impersonal expressions above, it was "you" before I backspaced and retyped it.
Any more knowledgable linguist or Francophone, please feel free to correct me. As far as I know this is all accurate, but I've never lived in a French-speaking nation to get the requisite first-hand experience. Here in America, I generally use
tu almost all the time, but I almost always am talking French with another college student or a high school student.