Major Site Update affected our Daily traffic

After updating our site we lost 50% of traffic.

[Kelcor]

The site has been up and running fine for over a week, but we have noticed that our Google traffic dropped off the following Monday, and keeps getting lower each day.

For the first time in a year I downloaded the Google tool bar, just to see our PR, which is now a 0 on the home page, but still a PR 5 or 6 on some category pages. Many keywords that were once in the top 10 listings are now maybe in the top 10 pages – I know that PR is not as relevant anymore – But it just seems a little strange.

Many of our pages show just the page link and no description, and show post update cache, others with description show pre-update cache.

Are we simply caught in a Google "Sandbox" caused by them possibly crawling our site while it was down, or is it caused by the few content changes we made on every page?

Anyone else encountered this?