I have a concern before I sign up with adsense. I have a site where we deal with water (not really but a good analogy). We're all about clean water and not water that is filtered, flavored, chlorinated. In fact, it would be quite detrimental to have adds that pitch flavored water or chlorinated water on my site.
I know that I can filter out up to 200 URLs but I'm worried that might not be enough. So it comes down to how good is the Google technology for determining what's appropriate for my website and are there any ways I can measure it's accuracy?
Mat_Bastien is correct: If you want total control over who advertises on your site, find another solution--e.g., direct ad sales.
For what it's worth, I use AdSense on my travel site but not on my freelance writing site. Why? Because most writing-related ads are for vanity presses and other scams or near-scams. I wouldn't feel comfortable having such ads on my writing site, and I don't want to spend my time monitoring AdSense and blocking advertisers--just as you probably don't want to spend your time trying to keep ads for treated water, Scotch and water, or so-called "water sports" off your site. :-)
>> you can almost assure yourself of advertising for competitors
I only intend to run Adsense ads until the store and my own ad sales mechanisms were ready to roll. I'm strictly thinking of this as a quick revenue stream while I'm continuing to build content/traffic and setup the more traditional revenue streams.
I emailed Google to ask the same question and they responded with the expected "we cannot guarantee your results". They encouraged me to go through the signup process to see what sort of revenue I could be making and noting that I could cancel at any time.