I think the true test is if it is of value to your users, if it is, I would maybe place it in an obvious ad section
Well, here is the conundrum in all this about quality content and advertising.
Sure, Google is interested in a site that is useful to the visitor. But, let's face it. In most cases I would say people are creating useful websites to get something out of it. There are people pouring 1'000's of hours into websites that offer amazing free services. Are these creators expected to do all that work for absolutely nothing? Actually it's less than nothing, because they are paying for web-hosting services to keep the site going.
If you are creating informational/instructional websites that are not retail. Meaning having no sales on the site, then advertising should not be frowned upon at all. Of coarse, I do agree there are those who get greedy once they see money coming in and start adding more and more advertising until you cannot tell the advertising from the content. This I agree has to go and is going thanks to Panda. However, lets not swing the pendulum 180 degrees and go from too much advertising to allowing no advertising or extremely little. If in fact (there is no conformation on this) Google is penalizing for advertising than what is going to happen (I already see it happening in the SERPS) is big brand names and massive sites will be the only results when searching and mom and pop websites will disappear into obscurity.
The massive website with Millions of few per month, per week, per day even can easily get buy with next to no advertising at all because of the volume of traffic they have.
There are some incredibly useful websites out there created by the little guy. One person in their home sharing their expert knowledge on something that is incredibly useful to those who need the help. Should they be penalized for throwing up a little advertising here and there to make a little profit for their efforts?
Of coarse this is all speculation that stems from frustration.
The fight continues. I will not give up on a 10 year labor of love.