What is the risk, man-in-the-middle or otherwise, of unencrypted connections between 2 people who use the same ISP, in the same city? If we assume the ISP (and the copper wire that leads to them) is secure, is there a fairly limited risk level? (excluding government surveillance, NSA, etc.)
What do both parties use their computers for? If either machine is infected then it really doesn't matter if you live next door to each other or in separate continents. End points are leaky little beasts.
To be more specific, You need to share how the communications are taking place. Are you using Skype or some other IM program? Email? VoIP? Because some communications programs have encryption built in your communications Some content is transmitted and received more privately than others. Do you both use a VPN?
The next question is what is the cost of the content if it is discovered? If it has no value to either party, or cost to either party if it is revealed then you are pretty secure.
Security is about managing risk. If you're talking about valuable IP, etc. then you are pretty insecure if the communications application is not encrypted properly.
Ultimately the security/privacy is limited by the weakest link, typically the end point, which includes the user as well.