Do my own villages/cities interrupt my "longest road" in Catan?
You are correct. 

Your own cities do not affect your status towards the "Longest Road" You can view the official rules here, from pg. 9 (emphasis is mine).


  You can break an opponent’s road by building a settlement
  on an open intersection along his road!


On page 8, in the example, Emily has the longest road card with 7 segments.  She has two houses within those 7 segments.

This was also answered directly in the online FAQ as pointed out by @shemmon.