If I am running a full node, what can an adversary determine from sniffing the traffic to and from my node, or is it all encrypted?
The connections between nodes are not encrypted, there is no purpose as the Tangle is public.
The connection between your wallet and its node is encrypted if its URL starts with https instead of http. It is recommended and Trinity now requires TLS (HTTPS).
Data inside transactions can be encrypted.
The connections between a fullnode and light nodes through the rest-api may be encrypted or not. Using https is recommended, but not enforced.
If the communication isn't encrypted, an attacker may collect precise information about transactions requested by a particular IP address. In other words, an attacker will gain the ability to make correlation between transactions. This is problematic for the privacy of light node user.
The connections (TCP or UDP) between a fullnode and its neighbors aren't encrypted. The data transferred between fullnodes consist simply in transactions (i.e. public data). An attacker sniffing this traffic won't learn anything except IP of direct neighbors.