Not a common sight, but it does happen at lower altitudes depending on atmospheric conditions. Saw a FlyBe Dash-8 with a long trail passing over Strumble last weekend. Cruise altitude was 23,000 ft. Last year I saw a Saab 2000 on a similar route, again with a long trail. Of course props at high altitudes leave vapour trails just as jets do...have seen a Super King Air on more than one occasion with a pencil thin trail out behind it.
I'll leave the more technically minded to explain why it happens!
Ken