Create Folder Tree's for SharePoint Lists and Libraries

EnsureListFolderTree

function EnsureListFolderTree($web, $list, $folderName) {
    $curl = $list.RootFolder.ServerRelativeUrl
    $folders = $folderName.Replace("^/+","").Split("/")

    ForEach($fn in $folders) {
        $furl = $curl + "/" + $fn
        $f = $web.GetFolder($furl)
        if ($f.Exists -eq $false) {
            $f = $list.AddItem($curl, [Microsoft.SharePoint.SPFileSystemObjectType]::Folder, $fn)
            $f.Update()
            $f = $web.GetFolder($f.Folder.ServerRelativeUrl)
        }
        $curl = $f.ServerRelativeUrl
    }
    $f
}