It's basically not formal... But:
a) in my region, Silesia, it's perfectly fine when you talk that way to elderly people, elderly is a key word here. You can tell an old lady "wy idziecie" (you go), "wy widzicie" (you see), "świetnie się trzymacie" (you look great) - not only it's absolutely correct, it also shows your respect. However, I'm not sure if it follows that pattern in other parts of the country.
b) the word "państwo" - ladies and gentlemen. After that you can use the verb in two different forms. First, the safer one, is third person plural - "państwo widzą" (you see). It is very formal, suitable to e.g. speeches. The second form is second person plural (wy) - "państwo widzicie". Beware, though. It is rather a controversial form (I'm not fond of it, personally, however it is correct). It's suitalble for a quasi-formal situations (e.g. the lecturer talking to students who he knows well).
That makes so much sense! It's very confusing to someone who has studied other indo-European languages. Here is why:
You informal: tu (French), tú (Spanish), ты (Russian), ти (Ukrainian) etc... You formal: vous (French- also the plural form), вы (Russian), ви (Ukrainian)
Then I get confused because Mexican Spanish uses usted to be formal but Spain has a vosotros form, like the French, Russian, and Ukrainian. But I'm not sure if it's used the same. So you can see why I would automatically assume that wy in Polish is a formal or even formal plural hybrid way to say "you."
Oh, sure, I understand - but in Polish it doesn't work the same way, unfortunately. The usual manner is "Pan/Pani" + 3rd person singular ("jeśli pani pozwoli" - if you allow me) when talking to a single person or "Państwo" + 3rd person plural (SOMETIMES 2nd person plural) when talking to many people.
Indeed, we talk to strangers using pan/pani forms. With friends we use the regular second person forms. That's the rule of the thumb at least, I don't know if the cutoff point is the same as in Russian. On the Internet I often see people using the second person forms, even with strangers.
We don't use the literal word "ty" that often because of the tendency to drop personal pronouns. Perhaps that makes it less jarring, and at the same more tempting than the (longer) formal forms.
I've noticed a difference in usage between Russian and Polish honorifics. On the internet and in advertisements the "ty" prevails, unlike in Russian. That's probably due to the fact that you can't know whether you're adressing a man or a woman. But this distinction is irrelevant if you use the Russian formal you.
Not anymore, however it used to be so during the communist period, likely influenced by Russian.
"Y'all" will go through and be counted as correct as well. If you are having a hard time keeping the plural vs. non-plural translation straight in your head, this can help. This is how my French teacher in high school would help make it easier for us to remember the difference. Then again I also live in a state where "y'all" is common vocabulary, so I guess whatever works best for y'all ;)