Ancient thread that I will RAISE FROM THE DEAD... Just because this spiking stuff is largely ignored on this forum and it's one of the cheapest quick-fixes for audibly better sound there is.
Isolation spikes do work, but they are only a portion of the solution. As el Doug pointed out, when used by themselves they can actually do more harm than good. The point of a spike is to channel the vibrations from the component. However when the component is spiked and then merely placed on a table, vibrations may also travel into the component. A vibration sink is needed. Grokit has it exactly right... A nice thick piece of maple on it's own isolation spikes does a terrific job. The maple acts as a sink for both the vibration coming from the component, and the vibrations that may be present on your average dining table, shelf space shared with other components, etc. By spiking the component and spiking the maple, you are essentially suspending the vibration sink (the maple) between the component and whatever it is resting on.
Mapleshade Records has a whole theory on this that I generally agree with... Although I find that nice heavy brass spikes with a height and diameter of around an inch (which can be had for as little as $1.75 a spike) do just as good a job as some massive 2 pound brass "footer" at $90 for 3.
A nice DIY maple platform is very inexpensive. I'm making one right now for a Woo WA7 that's coming. I'll be using an 8"x8" piece of 2" thick rock maple, and some of the Sewell short spikes you can find on Amazon for $28 for a set of 8 (I'm splurging on those, but they are nice). Total cost should be roughly $40, including the finished wood.
Important note... Always use a 3-spike configuration for the isolation platform. This ensures it will sit evenly. With 4 spikes, there will be movement, even on what appears to be a flat surface. For the component you can use either 3 or 4 (assuming your platform is perfectly flat), but I still like to use 3, unless the component is small enough where 3 will cause it to be too easily upset. For the WA7, I'll probably use 4. But we'll see.