How does a clay bar work? Being thick here is it just a lump of clay you rub over the car?

Pretty much.... there's a lubricant spray that you need to put on first though.

http://www.autogeek.net/detailing-clay-bar.html
http://www.autopia-carcare.com/inf-clay.html

I used maguires clay that came with a spray bottle of lubricant and a microfibre cloth.
I was unsure as I thought it sounded like a bit of a gimmick and I didn't think it would remove much dirt. At first when I used it I was not convinced as the clay was sliding over the paint because of the lubricant and didn't feel like it was doing anything, then I looked at the state of it! Also you can feel the rough bits on the front doors getting smooth as you slide the clay over it. I washed it, clayed it polished it then used a high gloss sealant from Auto Glym.

Andy, just out of intrest... how much of the bottle of the clay lubricant did you use? I'd say i used about ½ the bottle.

On the topic of lube, just a spray nozzle bottle with washing up liquid diluted sould be fine? as I bought the clay seperatly.

half a bottle = half a litre ish? Dont supposes it hurts to use more.

Sounds good me thinks it would work wonders on my black Zed :D

I don't think I used that much, I had to do it in the sun so used a lot as it dried quickly, I probably used a quarter may be a bit more.

OK, was just curious. Better to use too much rather than too little in this case (IMO). :)

results look stunning! i might have to do this to my black zed. only problem with black is it gets very dusty very quickly