I recently used the phrase "not altogether dissimilar" in an e-mail. I didn't think it was strictly unique, but I thought it was fairly original to my style. Then I was reading some five-year-old stuff I'd written, and I saw myself use the phrase again. I had no idea I had acquired it so long ago.
So I did a Google search for it, and found 7,500 results. I was vaguely disappointed.
[Pedantic tangent: When "dissimilar" begins an adjectival phrase, folks seem to be evenly split as to whether the preposition should be "to" or "from". I prefer "from," but I'd love to know if either is strictly correct or incorrect.]
Someday I'm going to write something meaningful and understandable where every four- or five-word string is unique on Google. Then I'll probably consider my meaningless and pathetic life and shoot myself in the face. <.<