I  work in the legal department of a council in central London - and I prefer the method of addressing that Pam describes

Name
company
address

Dear (name)

It's what I was trained in (I did an LCCI Private Secretary's course)

but it's common for legal letters to be addressed

Firm
Address or DX address

FAO: Name of person

Dear Sirs

I tend to try to reply in the same way they've written to us, eg Dear Sirs - Dear Sirs, Dear Mr Hart - Dear Ms X, Dear Guy - Dear Jane

but we also sign off everything

for Borough Solicitor

and do some other quirky things that relate to old-fashioned local government practices, mixed with old fashioned legal ways, mixed with newer ones as we have a lot of quite young fee earners from New Zealand, Australia and South Africa, who have often acquired more informal working practices.

I'd say go with your boss, so long as details are included to get it to the right place, and grit your teeth if you're not happy

Where I tend to stick my neck out to defend my methods is over headers/page nos on documents - one fee earner kept trying to remove a lot of information and it was much harder to deal with photocopying/faxing her work as it was slower to check things hadn't slipped out of order.

Luci