The reward change for miners is 80%, 50 to 10 Gulden. This is where most of the new Gulden goes on bittrex, Witness change is 50%, 30 to 15. Witnesses, most will keep there coins and use it to increase the witness amount with compound interest feature.
Dev reward only drops 18% but all those coins are sold on blockhut. Blockhut will have less coins to sell after 1st July.

All the rewards will drop 50% every 4 years after this change.