UPDATE:

first of all, thank you to the 2 people who donated.

gmaxwell from the devs gave me some pointers, so I implemented them:

- removed send change "back to input", because this might confuse people
- address-label is shown, if you enter a change address, also warning if change address is not in wallet or invalid address
- you can now lock/unlock per right-click in the GUI (same as the new cli method "lockunspent")
- (un)select all is now a button to be easier recognizable
- confirmations is now a number, no more icons
- the calculation labels are now on top and also shown in send coins dialog (see screenshots)
- "priority" added (very low - very high): miners order transactions by priority when selecting which go into a block
   priority = coinage / transactionsize
   coinage = value * confirmations
- fee is now calculated for real (before it did not take min-fee into account)
  In order to be able to send a free transaction, you need to follow the rules:
     - transaction size must be < 10000 bytes
     - priority must be at least "medium"
     - any recipient must receive at least 0.01BTC
     - change must be either zero or at least 0.01BTC
  If you violate one rule you will see a min-fee and also the labels turn red:
  Bytes.Priority,Low Output,Change. Depending which rule you violated.
  Those 4 labels also have tool tips explaining this.
  Also remember that violating one of the first 2 rules means 0.0005 PER kilobyte min-fee,
  while violating one of the last 2 means 0.0005 min-fee only.
(Just for the record, I did not make those rules, if you dont like them complain to satoshi:)