Its good if you target your keywords carefully ::
ie. A webhosting company - dont target words like 'webhosting' 'uk webhosting' this will cost you loads as there will be loads of sites competing for them.
Rather - 'uk php hosting' 'london based webhosts' 'webhosting companies in london' - spread the cash on more targetted keywords - you will get less clicks on each one, but you will pay a cheaper price and the traffic will be more specific.