Mark, was just playing with the same part. Its an irLED, but the cool part, is that it works as a detector as well. Notice a small bump for a lens on one face?
These are what's under the black plastic of the opto interupter in my slot machine I'm trying to fix up. Anyway, as a detector you get about .6 volts when they are about an inch apart. Also might be same/similar to what's in an optical mouse (will take a close look nextime I open mine to clean it).
Yeah, as ane emiter they aren't the brightest. Looked at it through the digital camera, only a small dot looking staight at it. Didn't try it in a dark room, but don't think it'll illuminate much.