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Are you sure you kept the same titles, meta tags, h1, h2, etc ? Absolutely no modification on these elements ?
Did you accidentally leave sitewide noindex/nofollow robots meta tags in place? I've seen that happen before when having a development version of a site go live.
[edited by: coopster at 8:24 pm (utc) on Jun 14, 2010]
[edit reason] fixed misspelling [/edit]
When you search for a unique phrase that is present only on your homepage, what do you get?
are you sure internal links navigation has not been changed?
I wouldn't freak out and put the old site up unless it's already been 4-8 weeks.
A major thing I noticed in investigating the crash was that internal link size more than doubled in the wake of the redesign. Part of the jump was caused by going from a static, image-only top navigation section to a CSS-driven text link top nav with primary links going across the top, groups of secondary links dropping down on hover, and even tertiary links popping to the side when hovering over secondary links.