IPs tell you very little:
- Folks connect thru tor
- Folks connect thru firewalls (esp. mobile users)
- Folks have dynamic IPs
- They tell you nothing of actual usage
And, at best, they give you a current snapshot, not the whole history.
Yes, partly, but also get an idea of the actual number of users rather
than the volume or the number of TX. This is a rather different thing.
If we get a snapshot, that may be better than a history. If people get bitcoins and then never use them, this does nothing for the bitcoin economy other than reduce the number of bitcoins in circulation.
For similar reasons, the number of people transacting in bitcoins is likely more important than that number of people who own bitcoins.
For that I would likely just use Mtgox's information provided of approxmiatly 30,000 people with accounts that have traded bitcoins for currency within the past 30 days.
Assuming this is 25-75% of the number of people who "own" bitcoins, that puts us at around 40,000-100,000ish "users."
What are you going to do with this information?
I personally would like to know the number of bitcoin users in each local market. This would be a great statistic to use to explain how much of a market there is for brick & mortar stores to start accepting bitcoins.