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(This thread never had much hope anyway)

Matt - I understand your caution... In addition to perusing Merry's web-sites, wandering about in Soho can be useful... just find a pub you like the look of and go in.

A few general guidelines:
If the pub is full of unpleasant leather-clad beings who look as though they might want to deflower you, back out...
If you hear loud American accents above the general noise (sorry guys), leave immediately.
As a general rule of thumb, avoid the pubs on major tourist toroughfares - find the smaller ones on back streets that only Londoners know about.
Take your A-Z with you, but hide it in your coat pocket. A lot of my friends photocopy the page they need if it's a part of London they're unfamiliar with... Every Londoner owns one.
Feel free to turn on your heel and walk out of a place. After all, you may feel silly, but you will never see any of those strangers again.

Merry's advice about not drinking lager (and above all, *not* Budweiser) is worth taking. Drink bitter - you can often walk in to a pub and ask for a pint of bitter, and they will simply produce the pub specialty (this varies from pub to pub & the area you are in). If they ask you what type you want and you haven't a clue, don't waste time looking ignorant and umming and aahing - just point to the most prominent tap and say "Directors/Smiths/Tetleys/Speckled Hen of course" You can always try something different for your next pint.