Bitcoin wallet download Statistics

Because each Bitcoin user can operate multiple Bitcoin clients and wallets, and not every user runs the client constantly, it seems very difficult to gather data about the Bitcoin community.

It's clear that many people in the community will want to remain anonymous (for good reason, if they hold a large amount of value in their wallet), and that collection of statistics in the Bitcoin client app would not be a popular option. Having read about malware that mines bitcoins, it's even possible that botnets may run a bitcoin client too. Even if such a collection technique was palatable, it couldn't be depended upon.

If statistics were gathered on a per-user basis rather than a per-client basis, a whole new data set could provide valuable information to the community, such as growth, feature popularity/desirability, usage preferences etc. Is there any mechanism with which a substantial quantity of real user data could be (or is being) collected reliably? Facebook comes to mind as a possibility, but even Facebook is easy to create fake accounts in.