it's a bit annoying when you put together a +£25 basket (to get the free delivery) only to find out that you can't get that important part you wanted because it's out of stock.... and it'll cost you £3.50 postage when it's back in... d'oh!! happens to me every time i shop there.
In my experience if you just make up a £25 order including any stuff thats out of stock and just order it anyway then they give you free shipping on the bulk of the order and then ship the out of stock stuff for free when it comes back in stock.