Question
Last night we were enjoying a nice breeze in our living room (screen closed door open) suddenly we noticed literally HUNDREDS of these small gnat-like flies around our ceiling fan,on our walls and down the hallway.  We had been playing in our grassy front yard at dusk, and we have a huge sand volleyball court in the back yard.  There are about 8-10 of them hanging out on my backyard window now... boy they are hard to get pics of!

Answer
Christie,

Small gnat-like flies (midges) can originate from indoor sources as well as from outside. Fungus gnats can emerge from houseplant soil (see http://www.livingwithbugs.com/fungus_gnat.html for a drawing) and there are a number of midges that can enter houses from sources outside. If the house is well screened my guess is these are fungus gnats. If you have houseplants in the rooms where you see them try moving the pots and see if the flies move with the pots. Houseplant soil can be treated but re-potting is often the best solution. Post a follow up if you have questions.

Jack DeAngelis