Is it just me or does Google seem to be really bad at acquisitions and/or executing this sort of competitor-cloning operation? I don't know if they're below-average, but it seems that a year later, nothing you read about them doing has ever worked out. Except maybe Android.
They seem to bat maybe .200 with successes, but the thinking here is probably "Why not?". It costs them almost nothing, takes very minimal effort, and at worst creates another revenue stream for Google.
Google Maps was a successful acquisition/competitor clone. Google Finance is also successful (a clone of Yahoo Finance basically). Those are the only two others I can think of off the top of my head.
I don't think Google is particularly below average here though; I think it's just a risky strategy to clone something. You often miss a critical non-obvious piece of the puzzle, because only the surface of the business is visible when you're copying it.