Yeah, I like Sitecore Powershell Extensions and I saw someone doing something script-like so I thought I would venture out to the SPE docs and see what is supported. Low and behold both fast and index based queries are right outta box, sweet!:

Fast Query

$query = "fast:/sitecore/content//*[@HaystackField1 = 'Needle' or @HaystackField2 = 'Needle']"
Get-Item -Path "master:" -Language * -Query $query

I find the ability to search an index from SPE pretty powerful in many ways, one of the first being that it’s easier to read than trying to use something like Luke to determine if something exists in an index:

$root = (Get-Item "master:/sitecore/content/")
Find-Item -Index sitecore_master_index `
          -Criteria @{Filter = "DescendantOf"; Field = $root },
                    @{Filter = "Contains"; Field = "haystackfield1"; Value = "Needle"},
                    @{Filter = "Contains"; Field = "haystackfield2"; Value = "Needle"} |

SPE, you and I are becoming friends.

Hope this helps someone.