Google PPC vs. Yahoo PPC

After your website is created and published you will come to a crossroads, depending on previous activity on the site. Do you have traffic yet? Did you have traffic? Do you anticipate any return on investment from your site just sitting there?
Take a global view of your company. What is the average dollar amount for a sale? How many sales do you average on a daily basis? Are they new customers? Are they existing customers taking up sells? With this data you can determine how many visitors it would be before you would need a conversion to stay on the positive side of the profit scale. Regardless of what your business is, everyone advertises to make money, it's an investment.
Say you average $100 dollars profit per sale, and Google has a minimum cost of $2.00/click. You would need to make 1 sale out of every 50 visitors in order to stay positive. So your goal should be 2 sales out of every 50 paid visits. 1 sale for every 50 visitors would keep you even and you would know that you need to make adjustments.
Now that you have your goals set, you need to determine which search network you want to use. Google has by far the largest search network, aka the most traffic. Yahoo has been around the longest and has a very large following of Yahoo email users. Maybe not searched as much as Google but always in competition with the most unique daily visitors. This could lead to higher conversions depending on the region, and age group you are targeting. Google has the most competition for advertising spots, and people are starting to learn that you can pay to be in those spots rather than using the search algorithm to show up organically. However not every business that advertises on Google advertises on Yahoo as well, so there may be less competition for top spot, making your cost lower, traffic lower, and possibly lower conversions. Lets face it without traffic there is no opportunity for a sale, and without sales there is no reason to advertise. If you have $100/day budget you might wanna spend $75 on Google and $25 on Yahoo this way you can determine which of the search engines provide your business with the right mix of traffic and conversions.
There is no real answer to what is going to work, but the old saying "Don't put all your eggs in one basket" definitely stands strong here. Diversity is what is going to set you ahead of your competition, using the data you can compile from your experiments with PPC can really boost your confidence and the success of your business.