finding it fascinating to be honest!! - there is a significant improvement in growth rate. The set up was fairly easy in that we had the pallet wood to build the bed and lots of cow manure to fill it with. I'd already started off the salad leaves in modules to plant out so once the bed had settled down to around 30c it was just a matter of planting them.
Following Jack First's plan we have planted radishes, carrots, salad leaves and turnips which are all coming along really well. The spaces between the beds have been used to propagate other seeds such as peas and beans, cucumbers, flowers, squashes etc.. - also, I've taken blueberry cuttings in pots which are being bottom heated in the bed.
The only problem we seem to have is mice (or birds) which are pulling up tiny seedlings.