I remember when those were very popular in the '80s. I felt that they were comfortable for awhile, but my back would start to hurt from trying to keep myself up.
This is what I use all the time, both at work and at home. I'm fond of them, personally, and they keep me from slouching, which was causing elbow pain during typing.
W/r/t the geek cushion: I like it! I agree with the general pricing sentiments, however. My no-brainer point is probably US$50, however.
I have something that seems to be the inverse of this: it's a special slanted table that's designed for using your laptop in bed. Some guy was selling them back in the late 90s, it was called the Laptop Laidback. His company is now a crusty component of the early dot-bomb fossil strata. I don't use the table that much, but it's a special luxury, as it's exceedingly comfortable. The most discomfort I have is trying to stay awake.