Quick note because it seems like a lot of people are looking for this. I was dealing with a badly behaving feature but had to find all the places it was installed on a fairly ornate farm. Here’s what I finally came up with:
Get-SPSite -limit ALL | Get-SPWeb -limit ALL | foreach{ $_.features["GUID"] } | select Parent
This will give you the site names where the feature is installed. The GUID is the ID of the feature. It could use some more work, specifically returning status and URL, but this will get you 90% of the way there.