Quoting an email I sent recently...
With bitcoin, every transaction is written to a globally public log,
and the lineage of each coin is fully traceable from transaction to
transaction. Thus, transaction flow is easily visible to well-known
network analysis techniques, already employed in the field by
FBI/NSA/CIA/etc. to detect suspicious money flows and "chatter." With
Gavin, bitcoin lead developer, speaking at a CIA conference this
month, it is not a stretch to surmise that the CIA likely already
classifies bitcoin as open source intelligence (no pun intended).
[...]
Attempting major illicit transactions with bitcoin, given existing
statistical analysis techniques deployed in the field by law
enforcement, is pretty damned dumb.