Just in case anyone is wondering: pasting discussion from http://lifein19x19.com to SL can be time-consuming if you manually replace each occurrence of :w1: with , :bc: with , etc. I've made a Python script which gets the task down to a few seconds per page. This is custom made for Bill's posts and would need more work to convert it to a generic tool (I haven't caught all the special characters, and was too lazy to parse the "quote" tag properly). Use at own risk!

#! /usr/bin/python3

# Read one of Bill Spight's posts
# and reformat the text for SL

# Replacements needed include:
#  :w5: change to W5 and sim for other numbers
#  :w21: change to W21 and sim for other numbers
#  :wc: change to WC
#  all of the above with b/B instead of w/W
# [b]something[/b] change to __something__
# [i]something[/i] change to ''something''
# delete [quote], [/quote], [go], [/go]

import sys, os, re

infile = sys.argv[1]
outfile = sys.argv[2]

if (os.path.exists(outfile)):
  sys.exit("Error: output file " + outfile + " already exists.")

with open(infile, 'r') as file:
  text = file.read()

text = text.replace('[b]', '__')
text = text.replace('[/b]', '__')
text = text.replace('[i]', "''")
text = text.replace('[/i]', "''")
text = text.replace(':wc:', 'WC')
text = text.replace(':bc:', 'BC')
text = text.replace(':wt:', 'WT')
text = text.replace(':bt:', 'BT')
text = text.replace('[go]', '')
text = text.replace('[/go]', '')
text = text.replace('[quote="Bill Spight"]', '')
text = text.replace('[/quote]', '')
text = text.replace('[hide]', '')
text = text.replace('[/hide]', '')

text = re.sub("(:w)([0-9]*)(:)", r"W\2", text)
# note r for raw string, so that \2 is interpreted as a backreference not as unicode character number 2!
text = re.sub("(:b)([0-9]*)(:)", r"B\2", text)

with open(outfile, 'w') as file:
  file.write(text)