For example, if a single Electrum seed was used to deterministically generate address A and address B, would it be possible to somehow link the two addresses together and deduce that they are both owned by the same individual? (Of course this is assuming that both addresses are kept separate with no mixing of coins occurring between them.)
Assuming, of course, that your adversary does not have access to your master public key, deducing that the two addresses were produced from the same seed is roughly as difficult (mathematically) as stealing bitcoin from those addresses. It would involve solving four SHA256 preimages and the two discrete logarithms (which is what secures transaction signatures in bitcoin), and would in the process give the attacker access to your master private key as well.
If it were possible, there'd be far worse problems to be worrying about....
