"Reciprocity failure" in digital photography?

Slightly off topic but there's a lot of good knowledge here so I was hoping to take advantage of it.

Those of us who shot (or shoot) film are aware of reciprocity failure, as light levels get very low and exposure times increase the film doesn't behave as it does at 'normal' times and light levels.

Is there a digital photography equivalent? I ask because the other night we had a killer thunderstorm going on here, perfect for photography because the rain held off for a good hour. This was also the first time I've don this kind of shooting with the digital camera. So I grabbed the tripod and camera (canon 40d) and went outside. Set the camera to iso 200 aperture between ƒ/13 and ƒ/8 pointed to the sky and held the shutter open. Exposure times were anywhere from 15 secs to 90 secs and like I said the shots were good.

However once I got them into Aperture I noticed what to me seems like more noise then I'd expect (and have seen with normal shots) for an iso 200 setting. Not enough noise to be a show stopper but still.

So that brings me to my question, do long exposure times/low light levels cause an increase in noise? And if so is there anyway to counter it in the camera?

thanks