Are there rough estimates how many people use bitcoin? And how much is the average amount they have?
That's really difficult to know. When most people ran their own node, node data (in the tens of thousands) would give that info. As the blockchain got larger, more and more moved to SPV (e.g., Electrum, Bitcoin Spinner) or to hosted (shared) EWallets (e.g., Instawallet.org, or exchange accounts) or to hybrid EWallets (e.g., Blockchain.info/wallet).
One thing that most every user with a node has it as least one unspent output. So we can know an upper bound. In February there were nearly 3 million unspent outputs:
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http://bitcoin.stackexchange.com/a/2849/153 That is likely an order of magnitude or more than the actual number of bitcoin users.
Blockchain.info reports 25K hybrid EWallets having been creating on their service. Some of these will be unfunded (either never used or all coins withdrawn and abandoned).
So sorry if this is of little help. That's the thing with a pseudonymous digital currency -- the data available or collected is of marginal use.
