No, the send-from address is not available, for a couple of reasons:
1) When people using a shared wallet service like MyBitcoin or MtGox send payments the "from address" could belong to any of the other users of the service (or could be a "change" address that doesn't belong to anybody). It is a bad idea to think that "address == person".
2) If more complicated transaction types are ever "turned on" in bitcoin, there might be more than one "from address". Satoshi designed-in support for complicated transactions like "this payment can only be spent if 2 of these 3 keys sign the transaction". In that case, there would be two "from addresses".
If you need this to refund coins, you'll need to ask the customer for a refund address.