strange system corruption (freebsd 9.0)

[Ingrid Ditra]

Hi, folks!
I am in the middle of really creepy problem with my new FreeBSD box. I would appreciate any ideas about what the hell happened.

I've installed FreeBSD 9.0 from CD on IBM System x3550 server (with RAID-5 on 4 hard drives) and moved on it the most of config's from my old FreeBSD (8.2) box, and everything seemed working fine for some days. Long story short, today I realised, that I can't login nether through ssh or console, some third-party soft doesn't work, and most of utilities from base system doesn't work too. 
My /usr/sbin and /usr/libdata are completely gone, /usr/libexec is empty, /usr/bin contains only dtrace dir and librt.so.1 many files from /usr/bin are gone, /usr/src contains only directory with my kernconf (there was all sources) and /usr/ports contains only ports I've installed.
Time of access to all deleted or semi-deleted dirs is almost the same, but I didn't find any weird actions in logs. First, I thought that portsnap (runned by cron) somehow corrupted my system, but it was executed like eight hours earlier. 
No one but me has access to this box, so it's unlikely mean joke.

So, please, please, help me. I really do not know what I suppose to do now. I can't find out why this happened, so it would be useless just reinstall system -- I'll have this situation again. All this stuff repeated twice -- so it is not kind of glitch (last time a cvsuped sources and ports and thought it was the reason of crash).