Valve has posted the results of their user serveys on the Steam website.

Episode Two includes a reporting mechanism which tells us details about how people are playing the game. We’re sharing the data we collect because we think people will find it interesting, and because we expect to spot emergent problems earlier, and ultimately build better products and experiences as a result.

These statistics show how long players took to complete Episode Two, average deaths per map, which advanced rendering options were enabled, and a whole lot more. They even have color-coded "topographical" maps that show where in the map most players died.

Unfortunately, there doesn’t appear to be any Portal-specific data.

Steam stats page:
Episode Two gameplay stats:
Results of Steam hardware survey: