Can a desktop wallet be tracked using IP address? I'm wondering if I use a vanilla desktop wallet like MultiBit or Bitcoin Core to send and receive bitcoins, who can track my IP address and how?
Surveillance nodes in the Bitcoin network that mass-connect to many nodes within the network could pin-point and identify your node as the first relay for some of your transactions with some degree of confidence. 

Receiving is not so much of an issue.

But spending from the same address consistently will enable surveillance nodes to figure out that a certain IP address is in control of some address.