In a recent report, industry analyst eMarketer projects that the U.S. online advertising market will grow a great deal in 2011 – with spending increasing 20.2% to $31.3 billion by the end of the year. That’s a significant jump from last year when spending reached $26 billion – a 14.9% jump.

Although future increases aren’t expected to be as high, it’s a strong reminder about the power of the Internet in a down economy. People want opportunities, relevance, targeted marketing and measurement. Internet advertising delivers at all levels.

But the key isn’t to just spend the money and measure it. Businesses that look at these opportunities need to think long and hard about what they’re doing. A misstep along the way can doom the campaign.

Here are some tough questions to ask:

What is my brand?
Who am I trying to reach?
How will I measure success?
How does that affect my marketing objectives?
Will this impact my company’s bottom line? Can I prove it?
What am I promoting that’s better than what the other guy offers?
Who is making my creative? Does it really work?
What happens when they reach my landing page? Is it new or something refined?

“The internet has become as fundamental as television to advertisers,” said eMarketer principal analyst David Hallerman. “As consumers continue to increase their time spent online and as the resurgent economy continues to bolster ad budgets, we’re going to continue to see an influx of dollars toward the internet. More ad formats, such as video, and more channels, especially social media and mobile, are also key contributors to the spending gains.”