A few days ago, I was trying to find all instances of a value stored in AD. I was trying to understand all of the places that a particular partial GUID value was being used. so I had to come up with a way to search all properties for all objects across the directory space.
[string]$value = "whatever"
([adsisearcher]'cn=*').FindAll() | % { If ($_.Properties.Values | ? { $_ -match $value}) { $_ }}
Happy searching!