The question was asked of how to change the inheritance of subsites under a site collection via PowerShell, as there could be a ton of sites under the root. Turns out, it's not too hard. Check out the script below. This sets all the subsites to inherit...
# get the site collection
$spSite = Get-SPSite -Identity "http://sitecollection"
# loop through all the webs in the site collection
foreach ($spWeb in $spSite.AllWebs)
{
# check if root web as this one doesn't obviously inherit
if (!$spWeb.IsRootWeb)
{
# grab a Navigation object
$spWebNavigation = $spWeb.Navigation
# change to true
$spWebNavigation.UseShared = $true
}
# cleanup
$spWeb.Dispose()
}
# cleanup
$spSite.Dispose()