Coinbase is a step up from Instawallet in terms of both complexity and security. But it is still basic with only standard sending and receiving functionality. Nevertheless, Coinbase has two features which make it a very convenient wallet for the beginning user.
First, the wallet allows you to avoid dealing with Bitcoin addresses entirely and instead send directly to an email address. This makes the transfer internally if both parties have a Coinbase account and if the receiver does not then it sends an email message to the recipient instructing them to immediately create an account to receive the bitcoin payment.
Second, Coinbase includes its own built-in bitcoin exchange which empowers users to convert between bitcoins and US dollars directly through their bank accounts using ACH and they have processed tens of millions of dollars worth of orders. Unfortunately, the bank account integration is only available with banks inside the United States and only a limited amount can be bought or sold at a time depending on verification and other Coinbase policies.
Third, there is a Coinbase Android app. Many wallets are cross-platform compatible.
Coinbase does not claim to be trust-free and all bitcoins are stored in a centralized location controlled by its operators. This means you do not have absolute control over your bitcoins and there have been technical incidents which have left users without wallet functionality, unconfirmed transactions and may have comprised data or personal information. But so far no customer funds have been lost and these appear merely as growing pains for this new startup.
Nevertheless, Coinbase raised $5m of venture capital funding and will likely be around the Bitcoin ecosystem for the foreseeable future and the founder and venture capital investors are unlikely to betray their users by absconding with bitcoins. Their current corporate policy of storing 85% of users’ funds in offline cold storage means that the bitcoins are likely well-protected against third-party theft.