Bitcoin is a very nice system, but the program's interface could have a little work. Here is my concept of the interface (somewhat inspired by a some proprietary payment system's Windows interface):
Instead of separate tabs for 4 kinds of transactions, we have four "filter" options":
1. All transactions / Sent or Received transactions / Sent only / Received only.
These work just like the tabs above.
2. Today / Last 3 days / Last week / Last month / Last quarter / Last year / All time
This filter allows you to see only the recent transactions, and also is a nice way of cleaning the transaction list for the user.
3. All receiving addresses (works only when "Received only" is chosen) / (list of receiving addresses)
Allows you to easily sort received transactions by the address they were sent to.
4. All recipient addresses (works only when "Send only" is chosen, supposed to take the place of button #3)
Allows you to sort the transactions by the address you sent them to.
The text boxes "n/unconfirmed" and "n confirmations" are replaced by images, followed by a number of confirmations. There is no image for transaction with extensively large amount of confirmations (it may be 100 or 1000, but for sake of illustration, the "secure" icon is just at last 3 "confirmed" transactions)
(those grey transactions are NOT supposed to be shown at all, but are shown semitransparent for the sake of illustration)
The balance needs some currency indication, so the new users don't think the balance is in dollars/euros/pounds/yen/anything else.
The second tab is "Address Book". It works the same way as the "Sending" part of the address book button on the toolbar. An extra button "Transactions..." switches to the first tab, sets the filter 1 to "Sent only" and filter 4 to the address that was selected by the time the button is pressed.
The third tab is "Transaction Options". It probably will contain such options as:
"[X] Add transaction fees to transactions automatically" (with no extra message box)
"Default transaction fee per KB: [0.01]"
"[ ] Allow modifying transaction fees for separate transactions" (with a message box like "Warning! Setting transaction fees as too low will result in your transactions being done slower." and respectively a new input field in "Send Coins" dialog)
"[X] Create a new receiving address after each transaction received" (so if someone turns it off, no extra addresses will be automatically created)