SharePoint 2010 finding web parts on the home page

Today I had to working on a situation where we need to replace a web part with a different one.

First step is to determine what pages have this web part on them. In our environment the web part was only added to the home page of a site. So the script assumes this is the only location of this particular web part

Here is the powershell script I used:
NOTE: I found a bug in that it may return ErrorWebPart. This is due to the httpcontext not being set.
I have modified the code accordingly(reference: http://social.msdn.microsoft.com/Forums/en-US/sharepointdevelopment/thread/607f3980-53c0-4007-bb34-9969ed6ea4fc)

Add-PSSnapin "Microsoft.SharePoint.PowerShell" -ErrorAction SilentlyContinue
# web application to crawl through
$webApp = "http://webapplication"
# output file for later reviewal
$outputFile = "C:\outputFile.txt"
# webpart full name - not the title
$webPartFQN = "assembly.webpart.name"

write-host "Reading from webapp $($webApp)"
$site = Get-SPWebApplication $webApp | Get-SPSite -limit All
# loop through all the site collection in the web application
foreach($s in $site)
{
  #loop through all the webs in the site collection
  foreach($web in $s.AllWebs)
  {
    if ($null -eq [System.Web.HttpContext]::Current){
     $isContextNull = $true;
     $sw = New-Object System.IO.StringWriter;
     $resp = New-Object System.Web.HttpResponse $sw;
     $req = New-Object System.Web.HttpRequest "", $web.Url, "";
     $htc = New-Object System.Web.HttpContext $req, $resp;
     #explicitly cast $web to spweb object else sharepoint will     #see it as a PSObject     $htc.Items["HttpHandlerSPWeb"] = $web -as [Microsoft.SharePoint.SPweb];
     [System.Web.HttpContext]::Current = $htc;
     if ($sw -ne $null){
     $sw.Dispose()
    }
   } else {
     Write-Host "HttpContext already set";
  }
    Try{
        # get the welcome page in the web's rootfolder.
        $defPage = $web.RootFolder.WelcomePage

        if( $defPage -eq $null -or $defPage -eq "")
        {
          #didn't find a welcome page, loop through all pages in rootfolder then
          foreach($f in $web.RootFolder.Files)
          {
            CheckForWP( "$($web.url)/$($f.Name)")
          }
        }
        else
        {
            #process page to check if the webpart exists 
            CheckForWP( "$($web.url)/$($defPage)")
        }
    }Catch{
     [Exception]
      write-host "Exception thrown while opening web{$($web)} and web part manager."
      write-host $_
    }  }
}
function CheckForWP($page)
{
   $pageUrl = $page                
   # Get the webpart manager to find all the webparts on the page.
   $webpartmanager=$web.GetLimitedWebPartManager($pageUrl,  [System.Web.UI.WebControls.WebParts.PersonalizationScope]::Shared)
   if( $webpartmanager -ne $null)
   {
     #loop through the web parts
     foreach($wp in $webpartmanager.webparts)
     {
       # get the title and name of the webpart
       $wpt  = $wp.Title
       $wpn = $wp.ToString()
       if($wpn.ToLower() -eq $webPartFQN)
       {
         #write out that I found the webpart in question and the webpart names
         write-host "Found on: $($pageUrl)"
         $pageUrl | Out-File $outputFile -Append
         " $($wpt)" | Out-File $outputFile -Append        
         " $($wpn)" | Out-File $outputFile -Append
       }
     }  
   } else {
     write-host "failed to get webartmanager"
   }
}