Publishing something online isn't as easy as it used to be. Back in the day, you could monetize traffic in a way where eyeballs == serious revenue. Not so easy these days.
On one hand, the growth of the Internet means there are more people out there to look at your stuff. On the other hand, there are more people putting out the same stuff as you. Increased competition makes it seriously tough to start anything new. I'm lucky because my sites have been around for five years or more, so they're established, but I can't imagine trying to break into a new space and be successful in any reasonable amount of time.
Then there's the issue of trying to fill ad inventory. In the late 90's you could make a mint with the various agencies out there. Then during the bust, most of them went under. Back in 2001, I nearly lost my shirt running CoasterBuzz.com, when bandwidth was costing me a grand a month and the ad agencies were dropping like flies. I had to start the CoasterBuzz Club in order to survive back then. That got me through the toughest time, and maybe this will be the year that I finally ditch all of that business debt (provided I keep working contract jobs on the side).
Pundits have been predicting the death of online advertising for years, but it is on the upswing in terms of overall volume, even though it has to be spread around more. Big advertisers are finally coming around to see that the mighty click-through is a shitty metric, and that, even on the Web, branding is a powerful tool without a specific action when the ad is viewed. They're finally realizing that, yes, just like seeing a billboard on the way to work, it's not going to result in the instant purchase of a car or a beer.
I do a little selling myself every year, but generally don't pull down more than a couple of grand. I just don't have the time. I'm still somewhat loyal to Burst Media after all of these years. I've been with them since 1998, and they survived the bust. They're still focused on the publisher as the first customer. Their ability to fill inventory is up and down depending on the month and the categorization of your site, but I can't easily break away from them unless they're losing money.
I also mix it up with FastClick, Tribal Fusion, Google at times, and most recently, Casale Media. I wrote an ad serving package (CliqueSite.Ads, download it here) that can rotate these providers with my own sales, and so far that's allowing me to tune things a bit with the distribution of inventory.
If you have something compelling enough, you can certainly make a buck, but it's hard to find a niche that you can own. Simply getting a good rank on Google isn't enough.
I love online content. It has more or less been my only source of income in the last year, during the time I was writing my book. There are college kids out there blogging about cell phone gadgets pulling down a couple of G's a month. It's such a change from my media roots (I double majored in journalism and radio/TV, worked in the biz for four years), where you needed a transmitter to make a living. While there's a lot of crap out there, and it's hard to separate the bullshit from the gold, it is an exciting time to be an online publisher.