Most of people I know are registered on several exchanges. While it is nice to have an overall view of balances, it would be also nice to knows what are our balances on each exchange.
Transactions are associated with an exchange already, as well as fiat deposit/withdrawal. We are only missing a view or a breakdown of how much currency we have on each exchange.
Additionally, the fiat value of each coin should use the conversion price on the exchange on which they are when possible: if I have 0.1Btc on Bitfinex and 0.1btc on kraken, the fiat value need to take into account btc/usd rate on both exchanges (as if I would sell coin at their respective location).