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Okay, then let's try to figure out how many bitcoins are owned by someone who just made a recent tx. b91a9fa769b1a401cb5ccd291cd99ff76d530d2fd22f597e743f7c169673bcd8 will do nicely. The two outputs contain 0.17323 and 2.08772 BTC, in that order. Considering there are many wallets out there that will put the change output last, and there is only one input, I think it's safe to assume the .17323 was sent to someone else, while the 2.08772 is still owned by the transactor. The change address has not been used for any other transactions, so we can't get any more information there.
Let's look at the source of those 2.6105 BTC then, 1BjEjcT3Z89pm6r3fRYhdpb43ySUg4Hc1n. The owner of this address is likely owner of the 2.08772 BTC change output. But what more can we discover? This address has only received bitcoins once, from tx ed504fe450deff23e1afa210fb96b0a3cfdced74da747f4bdda0d11440675211. Ah, again it seems this is a change address. Our mystery person started with 2.85938529 BTC, then made two spends, the .17323 mentioned earlier, and the newly discovered 0.59823529 out of this address. The interesting part now is that ed504... has two inputs, and it's highly likely that they belong to the same person.
I kept on following the transactions back in time, and they went a ways. I can be reasonably confident that 17ejmoBxMySL2hoDHgz8oCiv4BdRkxYFVr belongs to the person we're tracking, but its source of bitcoins would hint that our guy got paid at this address, and none of the other addresses in the tx are his. The same goes for 1Cy3HpsfEZEmRLQkZF8269mEzihXrkYeGe and 14wjT7byrZr7i4evq1gHWMdsurYAEtQJg4. With 1LqwYp6yiCwTBi5zsyob52CTRwNWCP6fH, we have the additional benefit of seeing that the address that funded it (1MxSAD) put its change back in itself, heavily implying that 1LqwYp and 1MxSAD are not owned by the same person.
So, what can we take away from this? If we were the recipients of the original transaction, and got this guy's shipping address, credit card number, name, and so on, what could we find out? Well, for one thing, considering all of these transactions have occurred today, it's likely this whole mess I've been looking through is some automated system. We're not yet at the point where individual people will on a daily basis make ~8 small payments purely in BTC. Perhaps it's dividends from a small security, or a bunch of people withdrawing funds from a web service. So if we got a name and shipping address for this, it might be reasonable to think that this guy runs a Bitcoin web service or something. We can also say that it's likely that at some point, this guy held about 2.997 BTC between some of his addresses, but is now down to 2.0877 BTC. However, we cannot say to whom the many outgoing transaction went. We won't be able to tell what other products or services he paid for. We also have based all of this off of educated guesses based on bitcoin amounts to change addresses, decimal precision, and the likelihood of two inputs being from the same person. There is a reasonable chance that we have switched up the guesses of spending and change at some point, which would invalidate so much of this analysis.
Overall, we can't pull out much more information, and we definitely cannot tell how many bitcoins this guy owns in total. It'll be at least .0877, but he may have many more. Heck, for all we know he could be Satoshi, sitting on a million coins from the early days. For me personally, if I were to give you one of my transactions, you would not come close to being able able to tell how many coins I own. Manage your coins well, and you can have a large impact on how well you can be tracked.