There are zero cases of Monero being traced. There are a handful of cases where additional information besides a signed transaction itself had been leaked by poor OPSEC. Address reuse is the most common leak. Addresses can't be seen on the blockchain, but they are seen by the payor. If payor A is an exchange that can identify you, and you gave the same receiving address to payor B, a DNM who's server gets seized, then the transactions can be linked by investigators. But the blockchain itself doesn't provide enough information to do this.