This wipe isn't unexpected. Blizzard noted at the beginning of beta that data would be reset at some point during the testing phase. The wipe coincides with what Blizz is calling a "pretty major" beta patch, the details of which will be revealed in the near future. Once the wipe goes through, testers in Hearthstone will be effectively starting the game as new players.
For those that spent real money on card packs, Blizzard is reimbursing the value via in-game gold. Those players will be able to purchase the same number of packs and arena tickets without paying a second time, though replacing the exact cards is not a guarantee due to the random nature of the packs. This is the last planned reset for Hearthstone; Blizzard is aiming for a full release before the end of the year so no further progress wipes are expected through beta and launch.