This is more a reply to Callsign's post. The unique factor that makes paid search such an appealing advertising medium is that it is completely trackable and you can easily see your conversion rate/cost per conversion etc. The BIG drawback with it (and this is entirely Google's fault - though unintentional I think as they are just trying to make it user friendly) is that anyone can get set up and start using it - and can get quite good at it, but usually only after several months learning and every mistake costing you x amount of money...
I would suggest getting your head around Google's excellent learning centre and in particular reading chapter 4 on analytics - (
http://www.google.com/intl/en_uk/adw....html#section4)
But make sure you keep track of your costs verus business generated - if in doubt contact a REPUTABLE SEM agency and ask them to do a PPC overview report for you - if they're of any standing they should give you the advice without any charge and can advise on any basic pointers your account could benefit from.