So PPC advertising is fast. With some systems, such as Google Adwords, you can generate targeted traffic within a few minutes of opening an account.

PPC advertising is also nimble. Where natural search engine marketing or other forms of advertising can lag weeks or months behind changing audience behavior, you can adjust most pay-per-click campaigns in hours or days. That provides unmatched ability to adjust to market conditions.

PPC can also be a bargain. Sometimes, you can find keyword 'niches' for which the top bid is around £0.10 - in that case, PPC is a great option, because you can generate traffic to your site for a fraction of the cost of any other form of paid advertising.

PPC advertising can cost a fortune. It's easy to get caught up in a bidding war over a particular keyphrase and end up spending far more than your potential return. Some PPC engines, such as Yahoo!, offer management features such as 'autobid' that will automatically increase your bid amount to maintain a particular rank. That sounds great on its face, but it can get expensive in a big hurry.

Also, ROI can be very hard to measure. Some PPC engines (Adwords and Yahoo!, specifically) provide conversion measurement tools, so that you can track whether your pay-per-click campaigns are generating the desired result. But these tracking tools aren't 100% accurate, and some of the smaller PPC providers don't deliver any conversion tracking.

And watch out for junk traffic. Most pay-per-click services distribute a segment of their results to several search engines. While you certainly want your listing displayed on Google and/or Yahoo!, you may not want your listings showing up and generating clicks from some of the deeper, darker corners of the Internet. The resulting traffic may look good in statistics reports but is very unlikely to generate a return.

Finally, pay-per-click advertising does not scale. If you get more traffic, you pay more money in direct proportion to that traffic - your cost per click stays constant, and your overall cost increases. Compare that to natural search engine optimisation, where you invest a fixed amount of time and/or money to achieve a better rank, and your cost per click goes down as you draw more traffic.

Most businesses can't afford to solely rely on PPC advertising. It's too expensive, and bid amounts inevitably climb. But pay-per-click can fill a few important roles:

1. Campaign and issue-based traffic.
   If you have a short-term campaign for a new product, service or special issue, pay-per-click can be a great way to generate buzz. You can start a pay-per-click campaign within, at most, 24-48 hours, and you can generally change the text of your ad in mid-campaign, so adjusting your message is easy. If you need to focus attention for a finite amount of time, PPC is perfect.
2. Direct response business.
   If you sell a product or offer a service that people can purchase the moment they arrive at your website, pay-per-click is a great tool. Online stores are a great example: You know that each click generated is a real potential customer, so spending money to increase the number of clicks makes sense.
3. Niche terms.
   If you are trying to generate traffic for a highly specific keyword phrase, PPC can often provide bargains. For example, you might not want to pay the top bid for 'driving school', but 'driving school kidderminster' is probably a lot less expensive.

Focus, focus, focus! Organic search engine optimisation is a PR-based, long-term attempt to grow your brand and image. Pay-per-click advertising, however, should be handled like any other form of paid advertising: Gingerly, and with a clear, quantifiable short or medium-term goal in mind. In other words, concentrate on conversions, not clicks.