I'm not sure what is meant necessarily by clustering (what you think it is)? However, there are analytics that look at transactions that are of equal amounts (or similar). These can be grouped together, say someone sends 100 Bitcoin in a transaction, it'll probably stand out against the rest won't it for that day.
Timing is obviously important, if something is sent as soon as it is recieved, then it's more than likely the person sent coins to themselves in a hop or a service (which usually have a large amount of coins in one address).
There's also master public keys that link wallets together, I assume ether has the same.
I'm using Bitcoin as an example, it'll be the same for ether though.
Some exchanges make it particularly difficult to follow. With Kraken you can generate a key every time you want to transact. I think that is quite untraceable, but I would like someone with good knowledge to show me I am wrong.