some feedback/questions: I just checked out multibit for the first time together with my brother (recovered some coins from an old electrum wallet and we imported a private key).

• How is the change address chosen? It seems (unlike satoshi client), multibit does not generate new addresses on it's own but uses some existing address for change. Why is that? I'm assuming to solve the "wallet backup problem"?
  
  The change address used is the address of the first transaction input consumed. This is mainly for simplicity but yes it does solve the wallet backup problem (at the cost of some anonymity).
  
  
• It seems funds are unspendable until the previous tx is in a block. Why? (this could be pretty annoying, say in case I want to send money to multiple different recipients. I would have to wait for a block in between each transaction)
  
  This is in currently because MultiBit does not have all the transactions to crosscheck that the transaction inputs are actually spendable. Talking to Jan (BitcoinSpinner) at the conference he mentioned that it IS possible to spend your unconfirmed change without it causing problems to downstream transactions so I plan to look into doing this.
  The reason it is in there is that I don't want transaction inputs that are unconfirmed to "percolate" through to chained transactions. In that situation you can have a chain of unconfirmed transactions all waiting on the very first. (If the first transaction was dust you could have a whole chain waiting for a LONG time and it creates a very poor user experience). Bitcoinspinner has access to all the transactions in a db I think so the situation is not quite the same so I need to test it out thoroughly.
  
  
• A suggestion regarding key import: I expected to be able to import a private key by pasting it into some textentry field. Instead we had to generate a file (we u
  
  

sed key export to see what the format was). We didn't know what to use for the date and so we used todays date. As we later discovered this was a mistake, we should've entered the date the last tx on that address had taken place (we did a blockchain rescan afterwards to fix it). So the suggestion: in addition to being able to import keys from file, maybe a textbox to paste a private key could be offered. After that, a popup or something could ask for the rescan-timepoint and explain what it is about)

The MultiBit key export/ import is designed primarily for backing up the MultiBit wallets and giving people the actual key values. I agree it would need more work before it was a general purpose key import tool.
The main limitation is that MultiBit (currently) needs to go back and redownload and replay all the blocks from the key's "birth". It does not store all the transactions, only the ones for EXISTING wallet keys. When I do an import I need to know the age of the key. For keys coming from a MultiBit wallet I know the age of the private key and hence can write it out with the key data. (That is why it is a file and not a text box).

An example of this: Piuk (blockchain.info) wrote some import code for MultiBit for his encrypted wallet backups he mails out when you do a spend on blockchain.info. Unfortunately he does not keep the age of the key so when I import one of his wallet backups I have to go right back to the genesis block and reload all the blocks. This is incredibly slow. If it  "gets you out of an emergency" it is acceptable but for general use it is not really quick enough.


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A sort-of bug (likely not multibit fault, probably not even fixable from multibit source): My brother uses a window manager called "notion" (formerly "ion"). At times something gets screwed up and menus (both when selecting from main menu and also the context menu when using right-click on, for example, a transaction) appear offset to the lower right (by many pixels, somewhere completely else in the window) and menu items cannot be selected with the mouse. Once it starts occuring it keeps occuring with the same offset. A frame-resize doesn't help, but putting multibit into another frame (re-attach) does. This might not be worth investigating since it's most likely notions fault, just thought I'd let you know anyway.
I am not sure I can do much about this one.
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Other than that our experience has been satisfying. Thanks for a great open product!