Cash sucks for serious money laundering. It's fairly anonymous in small quantities but start talking about millions/ billions and it's bulky enough to be hard to transport across borders and each bill is tracked by serial number which means spending it involves a lot of leg work. Gold is way better than cash when it comes to money laundering.

PS: Drug kingpins have been known to dump small denomination bills as not worth the hassle.

I thought that was the main use of the $100 bill. Supposedly 2/3 of the $100 bills circulate outside the US [1], presumably for money laundering type activities.

[1] http://en.wikipedia.org/wiki/United_States_one_hundred-dolla...

US Cash is often used for Legal transactions outside the US. Basically, people often trust USD more than there local currency's. Either from inflation concerns or simply there ability to spend it outside of there home country.

Someone mentioned this in a bitcoin thread but money laundering is harder with cash than bitcoin for the simple fact that at one point somebody needs to take the physical bills.

A seller of an object must expose himself when he tries to collect his cash. With bitcoin, he can simply give a wallet.