This is a huge release, thanks to core dev team for all the hard work. There are few notable features that many were waiting for. Amonth others:
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Increase default -blockmaxsize/prioritysize to 750K/50K - maybe this will cause miners to include more transactions in blocks, so transactions will confirm faster
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Relay OP_RETURN data TxOut as standard transaction type - LOTS of potential in this change (it allows you to send small data snippets along with the transaction). It will enable things like Mastercoin, Colored coins, or Trusted transactions (an trusted service including its signature as an output which will allow other parties that trust this service to accept its transactions with lower amount or even with zero confirmations).
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Reject insanely high fees by default in 'sendrawtransaction' - I myself was stung by sending bigger transaction fee than I wanted to, hopefully this will prevent others from doing the same by mistake
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Prune provably-unspendable outputs - yay for reducing UTXO database size
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New default minrelaytxfee - finally. Paying ~5 US cents for every transaction, even small ones, wasn't that great. Half a cent sounds much better
