FWIW, I noticed one of my threads has also vanished.
Try a search on the forums for the terms "xin diagnosed yesterday". It will return references to URL:
www.cysticfibrosis.com/forums/messageview.cfm?catid=902
Following that URL, however, throws a:
<div class="FTQUOTE"><begin quote>ERROR: Sorry, we were unable to locate the object requested.
Error Code: 102 </end quote></div>
IOW, the thread was indexed at some point (thus the search result hits), but the thread itself is gone.
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Several sections of the thread are also living out on Google's cache:
<a target=_blank class=ftalternatingbarlinklarge href="http://webcache.googleusercontent.com/search?q=cache<img">http://webcache.googleusercont...com/search?q=cache<img</a> src="i/expressions/face-icon-small-blush.gif" border="0">ZcLxMRaql4J:www.cysticfibrosis.com/forums/messageview.cfm%3FFTVAR_FORUMVIEWTMP%3DSingle%26catid%3D902%26threadid%3D64508+site:cysticfibrosis.com+%22diagnosed+yesterday%22&cd=5&hl=en&ct=clnk&gl=us&client=firefox-a&source=www.google.com
(Search google.com for 'site:cysticfibrosis.com "diagnosed yesterday"'.)