Coming to this much later on...(sorry!) I would say that I always use:

Many thanks,

but I often have great fun trying to work out which faithfully, sincerely etc would go at the bottom of a formal letter, which I love to address as

To Whomsoever it may concern (rather than dear sir/madam)

and get repeatedly told off by proof-reading friends.

Many thanks,
from an over enthusiastic poster wink

----The next sentence is true. The previous sentence is false----