I just finished mine today, and I'm pretty pleased with it. You can feel every vibration the engine makes, which I think is what alot of people like about it.
Throttle response was good, power gain was marginal as far as the butt-dyno is concerned, but like strung said, 18lbs of car is gone.
All in all it took me about 3 hours to do by myself (that includes riding my bike to the tool store to get a tool that I broke) The hardest part by far is getting the dang oil pan off the engine block. Other than that, you just have to be willing to get dirty (really dirty) and know how to use a wrench.
We used to think if we gave a million monkeys typewriters, they would eventually come up with the complete works of Shakespeare. Now that we have the Internet, we know we were wrong.