Of course, four million wallets do not mean four million users. Some Reddit users claimed they have ten or more blockchain wallets. The exact number of users is hard to determine because Blockchain.info does not collect personal data of its customers. Coinbase claims its 3.8 million wallets belong to 2.5 million individual users.
Also have a wallet (or two) with them but have not used those in over a year. Have not looked at them in a while but security is still my main concern. Will just stick to my Trezor and Electrum.
Interesting figure from CoinBase, 2.5m individual users. Bitcoin is gaining more and more traction by the day.