google update in dec 2009?

Hi there,
i'm an italian webmaster, and my website is going bad from dec 2009.
So i thought that maybe an update has changed something in crawl
process o indexing.
I have approx 50K visitors per day, but i did very a lot more visitors
than now, and i think it's not google mayday -just because the date it
happened-.
Anyone had the same problem?

ps: i cannot give the url of the website because i'm consultant and
that's not my personal blog.

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