"Talking shit" can mean exactly the same thing as "talking bullshit", in the UK at least.
Talking bullshit would mean knowingly lying. John paid me for a service I told him I could perform, but I was bullshitting him when I said that. I can't actually perform the service. The mayor campaigned on lower taxes, but he knew he wouldn't be able to change that law.
Now, what I would be doing in a bar is "shooting the shit". This means you're just telling bullshit stories (wild, made up, inaccurate, designed purely for entertainment). I caught a 30" bluegill is bullshit, and I would only say that when I'm in a bar shooting the shit.
No, no, no! In the UK it is not uncommon! People over here are talking shit all the time, often not about anyone.
Though you may encounter the odd person in everyday life who is 'full of shit'.
Such is the British way, we tend to use these as terms of endearment just as much as genuine insults.
It amuses me to hear a US citizen use words and pronunciations I know are from the UK, just due to exposure to the BBC. In the US, Hyundai is pronounced "hun-die" or "hun-day", but I have a coworker who is very much an American who pronounces it "high-un-die" because the only time he hears the word is when watching Top Gear.
The Internet makes it difficult to tell which dialect the author is speaking, spawning these arguments and fostering communication between people 3000mi away from each other. That's a wonderful thing. Now if only I could figure out what a curry is and why everyone seems to love it over there.
[1] Harry G. Frankfurt, On Bullshit