Does AdSense decrease your site's earnings?

I've read several times that Adsense is basically a waste of time, mostly because you get paid shit and are directing people AWAY from your affiliate links. So, does anyone have any practical experience with this, or is it just speculation?

Has anyone ever run a test on one of their sites that actually showed Adsense hurting a site's earnings? Or did it perhaps increased the site's earnings?

Its how you look at it...
Adsense is good for micro niche sites which can be set up and left on autopilot pretty easily. Most big time adsense earners have hundreds of micro niche sites that bring in $2 to $10 per day each.
If you have a website that has a substantial amount of visitors who can be targeted with cpa or affiliate offers then adsense is a waste of time.
To put it in the bets possible way...adsense is more lucrative if you are going to build hundreds of different websites.

Thanks davioli, I like that reasoning.

In fact I am in the process of building 100+ little niche sites just like that -- starting off with 5-6 articles on each one, promoting them, and then possibly increasing the content on well performing sites to 30+ articles (all unique content).

How would you monetize something like that? Or rather, how would you incorporate affiliate/CPA offers into micro-niche sites, if at all?

Make sure the niches are really really targeted. Get the articles written based on even more obscure long tail keywords so that you have to get only a handful of backlinks to rank for each term. After that its simply on autopilot and you can just increase a few articles to each site every few weeks or so.
If a website is doing better than others...Id say around 3 to 4k uniques a month ...it would be good to sacrifice one adsense ad unit and have a very targeted CPA offer. Do not go for affiliate offers as they don't really do well.
One more thing to note is that adsense earning websites are very highly valued. You can create a hundred websites for now and after a few months start selling websites that are making 40 to 50 a month. You can usually get 10 times the monthly revenue and you can simply reinvest the money into a handful of other similar sites.

Oh ok, thanks man!

it's just depend how you see the things , if you have like 2 blogs with 3 visits per day ... it's normal to be worthless ... if you have 1500 blogs with same 3 visits per day each ... things can be seen from other shoes ... if you know what I mean ..