In the context of online advertising (most of us use Adwords nowadays), I think it’s very important to target differently based on where prospective clients are in the buying cycle.

Let’s say you sell iPod accessories.

You’ve – (overly simplified)

1. people that know they are searching for your accessories

2. people that already have iPods that are a good sweetspots (buying or reading about iTune, discussing other accessories, spending time in iPod usage conversations)

3.people that don’t have iPod.

While marketing to these groups online, you should come up with different offers, messaging, conversion goals … and in this case maybe opt for a “paid search campaign for group 1, placement targeting campaign in selective blogs and sites for group 2, and nothing or advertising on iPod selling sites for group 3.