By using the DirectorySearcher class we can build complex LDAP queries to find objects in Active Directory.   With this information you can do all kinds of fun scripting things.

Here is a sample script:

#Specify the search criteria
$samname = "jasonv"
$domain = "dev.lcl"

#Get a list of domains in the forest and grab the DN of the one matching the above parameter.
$forest = [System.DirectoryServices.ActiveDirectory.Forest]::GetCurrentForest()
$domain = $forest.Domains | ? {$_.Name -eq $domain}
$domainDN = $domain.GetDirectoryEntry().distinguishedName
Write-Output  "Found the remote domain, the full LDAP distinguished name is $DomainDN"

#Create an LDAP searcher object and pass in the DN of the domain we wish to query
$Searcher = New-Object System.DirectoryServices.DirectorySearcher([ADSI]"LDAP://$domainDN")

#Pass in the ceriteria we are searching for.
#In this case we're looking for users with a particular SAM name.
$Searcher.filter = "(&(objectCategory=person)(objectClass=user)(sAMAccountName= $samname))"
$results = $Searcher.Findall()

#Loop through the results
Foreach($result in $results){
    $User = $result.GetDirectoryEntry()
    $userDN =  $user.DistinguishedName
    Write-Output "Found a user matching with the distingused name of $userDN"
}