[rorrr]

What would stop me from creating a thousand (or a million) wallets, and just randomly shuffling money between them a thousand times per day, creating a visibility of activity?

As long as you control all the wallets, the money is still yours.

[Groxx]

Not much now, but if this becomes the norm, transaction fees will stop you. Or at least discourage heavily - excessive transactions aren't great for the network because they bloat the block chain. Mixers largely bypass this concern because they can deal with larger blocks of money and more people than you can realistically do yourself, so the transaction fees are basically inconsequential.

Also, if you do this, you're likely not forming a new TOR connection each time you do any transaction, so you're leaking your IP address and traffic - easy to gather and be reasonably confident that someone is doing precisely what you described, and since it's all recorded forever, all the actions are essentially tainted forever. If you do form a new connection each time, you'll slow down substantially, and there may be a way to block you at the entry points to the TOR network (I don't remember TOR's details well enough to be sure, though).

edit: also, this will be very easily identified behavior unless people do it all over the place (and then transaction fees are basically guaranteed soon after), so you'd stick out like a sore thumb. I would be willing to bet that while it would give you some anonymity and you might shake off a few addresses, you won't gain complete anonymity, and it'll probably ultimately be worse and slower and harder than just using a few mixers. And if you ever transact them in a way that re-forms those connections (if they're all millionths of a coin, it's unavoidable), you just undid almost all your work.

[rorrr]

If I send the money between my wallets, the transaction fees are not an issue - I keep that money, don't I?

Making a new TOR connection per transaction shouldn't be too hard to automate.

[Groxx]

They are an issue. Transaction fees are paid to the miner who builds the block which contains a transaction - for your transactions to be valid, they must be included in a block, so you'll have to pay the fees. Unless you mine the block yourself and don't require a fee / recollect it - a possibility, but your odds are abysmal.

Transaction fees are intended to be motivation to be a miner. Since 50 bitcoins per mined block will soon become 25 and eventually nothing, transaction fees will progressively take over to become the majority of miners' income. They're not enforced by the protocol, so there may be some transaction-fee-free miners out there at any given time, but they're not likely to be the majority of the compute power (and will probably diminish as time goes on). You might end up waiting for a long time for your transaction to be confirmed.

[michaelt]

If there's 1000 wallets that only transact with each other and never (or rarely) with other wallets, it might be possible to identify them as an island in the transaction graph - see [1] for an example of automatic graph clustering (I think the image is communities in facebook's social graph, but the same algorithm could be applied to a transaction graph)

Of course, whether that behavior would stand out depends on how other users of the system behave.

[1] http://www.ece.umd.edu/~wenjunlu/images/gephi.png

[rorrr]

You will probably find many of these islands even right now.

Plus, I can divide my 1000 wallets into 20 islands, and only have 1-2 transactions between the islands.