I went to see Filth at the theatre as well and I was rather impressed by it. I tend to get bored rather easily with monologues (which is rather ironic as I tend to write in them) so it was a pleasant surprise to enjoy it.
I do however think Trainspotting is the biggest load of tripe and is one of the few occasions where I prefer the film to the book itself.
Out of the few Welsh books I've read Glue has been the one I've enjoyed the most. Filth was rather good as well but the structure of that pissed me off slightly - the part where his "inner voice" speaks and is basically scrawled all over the book.

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[marquee]If my father gives me one more hint to tidy my room I'm ramming the fucking hoover up his arse

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Trying to be verbally ironic whatever the fuck that means