We haven't cleaned our window screens in so long and I'm glad that we finally decided to roll up our sleeves and do it this weekend.It didn't take long as we just took everything down, labeled them, and the sprayed them with the garden hose (high pressure) outside - we got to water the grass too! The windows took longer to clean but everything looks bright and squeaky clean.
When we took the screens down, we also found 2 which had holes - we've never noticed them because they're normally covered by shades and/or curtains - this explains the occasional fly / insect that we see inside the house.
I ran over to Home Depot to get a repair kit. Back when we were living in the condo, we've tried replacing the screen on a screen door and even though one has all the tools, it takes some practice to get the screen on nice and tight. This time, since the holes were small anyway, we decided to just use a patch. The best option available seemed to be a product called ScreenMend which sells for $7, it worked great. It should hold (these are not high-traffic screens anyway).