A friend asked me this question when I shared my idea of using one as a light probe. I replied by asking are they fast enough for what?
Here is my VCR remote control. The first track is channel up and the second is channel down. If you look close you can see differences in the patterns. The IR from the remote is easily picked up by the solar cell.
The second picture shows the fluorescent light in my basement and my computer monitor respectively. The monitor is set to 85 Hz, I was able to determine this in Audacity. Actually I got a value of 84.8 Hz, but I figure that's close enough.