I always blur out licence plates, often faces, you’ve never seen a kid here; I err on the side of caution.
You may not notice the information you’re giving away in a photo. Often it’s something in the background that sinks you.
I use an offline editor (like Photoshop) to edit before uploading.
If I’m using an online editor, like Picasa, I assume the file I’m altering is also available in its original form on some server, somewhere. Whether or not I post that photo, doesn’t matter, it still exists.
When editing, take the time to smudge and obscure, using many strokes of the mouse.
And absolutely do not use the swirl effect; all you have to do is reverse it, and look:
(photo via Wikipedia)
Interpol used this exact technique to locate and arrest a child molester , “Mr Swirl”, back in 2007.
I remember being in a room full of people when that came across the TV, and I said, “oh he used the Photoshop swirl to hide his face, reverse it”. Then the news story continued, and people looked at me like I was a wizard (easy crowd, totally milked it).