Bitcoin doesn't need to have a one-size fits all client / user model.  

Casual users might wish to use a javascript wallet, such as the My Wallet from http://Blockchain.info/wallet and http://StrongCoin.com (though know that both have fees when withdrawing).  Or a paper-based wallet -- http://www.bitaddress.org
Or a wallet on your mobile, like BitcoinSpinner, or BitPay (which is a mobile front-end to an Instawallet)

None of these methods require the Blockchain to be downloaded.