[Haskell-cafe] How to estimate number of downloads of GHC or Haskell Platform?

For a review, I'm trying to get a rough estimate of how many times GHC or the Haskell Platform have been downloaded. Although I'm sure I've seen this information graphed over time at workshops, my web-search skills are not turning up anything. I'd be quite happy to get an estimate to within a factor of ten. Can anyone suggest any sources, or a good way to estimate this number? Norman