Ventilation Sweet Spot...

When you build a tight house, you need to introduce fresh air to keep the indoor air healthy.  The advantages of using an Energy Recovery Ventilator (ERV) to bring in your fresh air are many:

-You know where your air exchanges are coming from, rather than counting on leakage.  Most traditional homes are getting their make up air from the least desirable places, like crawlspaces.  Turn on your clothes dryer and you are expelling 200 cfm of air.  Since you don't live in a vacuum, that air needs to be replaced from somewhere.  The path of least resistance in an existing home or poorly built new home is likely laced with camel cricket feces from the crawlspace, and maybe a little mold...

-Since you know where the air is coming from, you can filter it, and in some cases dehumidify as you bring in your fresh air.  

-You can exchange the energy of the outgoing "stale air" with the incoming fresh air.  For example, if it is 30 degrees outside and 70 degrees inside, you don't want to just pump 30 degree air into your house while pumping out all of that energy (heat) that you just paid for.  The "Energy Recovery" part of the equation means that the ERV captures roughly 85% of the energy in the outgoing air and introduces it to the incoming fresh air.  

-Fresh, filtered air provided by thoughtful air exchanges is good for your health!

Potential Pitfall- The only negative that I have run into using ERVs in the mixed humid climate of the Piedmont of North Carolina is over ventilation.  As you can imagine, if you bring in too much "fresh" air during the summer in this climate, you are bringing in a lot of humidity.  Conversely, during the winter, over ventilation results in an excessively dry indoor environment.  Most ERVs will let you adjust either the cubic feet per minute of flow, or percentage of time running per hour so that you can dial in your Air Changes Per Hour (ACH).  With an inexpensive humidistat and your nose, you should be able to find the sweet spot without getting overly scientific about it.  Everyone knows what a stale house smells like.  Avoid that.  At the same time, don't overdo the ventilation and make the level of humidity uncomfortable in your house.