Once I give him/her my bitcoins, I am now able to see how much he/she has in that particular wallet
No. You are now able to see how many XBT are on that _address_. Which is why there is a recommendation to always employ a new address for every transaction.
Thanks J, that's what I meant, you can now link that person to a specific address (not his entire fortune, just that specific address), and now see what he does with that money. Even if he's going to use different wallets to do different things, at some point he will use that money..
Let's imagine I give to a friend 1BTC because he sold to me his old laptop.. now there are two possibilities:
1. he will never mix the money in that wallet with the other BTC he has, but he will spend it someway and I will be able to see where the money goes..
2. he will mix that coin with other he already has (maybe to buy something more expensive than 1BTC) in a transaction.. now I am able not only to see where those bitcoins went, but also to link other address(es) to him and see where he got that money from, how much money he had in that address, other expenditures he had, etc.
Sure you can use a different address for each payment (ok, not so sure, read below) but at least I will be able to see where the money I sent goes. On a larger scale, this will be an issue also when/if a company pays the salary to an employee in bitcoins.. they will be able to monitor his transactions. Maybe he will use a different address each month, but the point is the same!
Last point, we can expect a person with an average/good computer knowledge to take precautions like changing address for every transaction, not from everyone. And my point is exactly that I see this as a possible obstacle to a larger adoption of Bitcoin.
What I want to understand is if this is a known issue which has been already addressed by the guys working on the protocol or by some kind of software..
I hope my thoughts are clearly explained! Thanks for your comments and help!