Block Quote: 823800

'The design outlines a lightweight client that does not need the full block chain.  In the design PDF it's called Simplified Payment Verification.  The lightweight client can send and receive transactions, it just can't generate blocks.  It does not need to trust a node to verify payments, it can still verify them itself. 
The lightweight client is not implemented yet, but the plan is to implement it when it's needed.  For now, everyone just runs a full network node.' July 14, 2010 - Satoshi Nakamoto