Our problem was two fold.

1) Sander Gerz describes a Google related Context.Rewrite() bug in ASP.Net 2.0 that occurs when the browser header User-Agent setting is Mozilla/ 5.0.  This happens to be the browser Google identifies itself as.  The error will result in your form failing when trying to write the action tag.  An Exception is thrown. Read the post to learn more about the specifics.

2) We had a custom error page that used Server.Transfer to display a friendly message when an error was caught by the Page_Error event on a failing page.  Unfortunately, the developers did not explicitly set the response code to 500 so Google thought that we were a website all about "Errors have occurred...".  They got a 200 OK status, after all.  Lesson: set the response code to 500 when showing a pretty error page.  This will likely result in some browsers not displaying the content but it will trigger the appropriate escalation chain attached to error events.  Sending a regular page is the same as swallowing errors in an empty catch...  not good.

So, read the post about rewritten paths and google in ASP.Net 2.0 and think carefully about how you handle errors.  It is a good idea to practice diagnosing a problem having a similar configuration to your target production environment so you can identify what you'll need when break down occurs.  That would include whatever restrictions your administrators place on you such as no machine or filesystem access or debugging.  Sometimes you really cannot recreate something in another context or environment until you'll identified the cause of a problem.

Hint: use the Exception Handling Application block from the 2.0 Enterprise Libraries