Every day is the date everybody should be celebrating it. Celebrating this once per year seems like a risky game to me. This should be the Golden Rule for holding Cryptocurrency Assets Safely. Never keep your Money under the Custody of some one else unless required. For example, Depositing only to Exchange your Bitcoin and then to Withdraw it is a mandatory transfer of Custody from you to the Exchange and back.
It's not a celebration. It's an event where people are encouraged to withdraw their funds from the exchange to prove solvency.
There are better ways to prove solvency; ie. known cold storage address and regular proof of solvency conducted by the exchange. This movement doesn't mean much because the amount of coins withdrawn and the number of people that are participating in it is minuscule and is by no means a good way to prove the solvency of an exchange.