How much advertising $ is enough?

I recently read a very open-ended question that was posted on a forum. It was simply "How much should I spend on advertising?" That's a good question. But, you can only answer the question in the context of:

• What are your advertising goals?
• Who is your target market?
• Where is your target market?
• How do you enter the conversation with your market?

Is the answer multi-millions, and you are spending like crazy to promote new software (e.g. the Windows XP roll-out a few years back, or the Microsoft Bing roll-out of late), or is the answer almost nothing, and you build through word-of-mouth (e.g. Apple's iPad).

You can't know how much you need to spend until you set your goals, build a strategy and a plan.

The next big question, is what is your return on advertising spend? Advertising should be an investment, not a cost.