I'm personally fine with Bitcointalk on mobile when I'm reading posts. The scrolling from left to right is easily fixed by using landscape mode on my phone. What bothers me a lot though, is when I'm posting or replying to quotes. Formatting quotes to make my reply look clean is too much of a hassle as you'd have to manually erase the irrelevant stuff.
Yes, this one seems to be the only issue for me when replying on mobile. Not that it cannot be done but it just eats time and also quite inconvenient.