The only risk to you is that I may have also signed that same bitcoin over to someone else.
More recently another risk emerged: The ability of the node to feed the user a different chain, and then proclaiming that this chain is Bitcoin - when it's not.
In this scenario, a userbase which relies heavily on a few nodes can be switched to any implementation the few node-owners want. So if a few node-owners collude, they can switch nearly the entire BTC userbase to another coin and then proclaim it BTC.
So nodes are important. Very important.