I find it interesting that you have to ask. If you go to a newspaper website, it's COVERED with ads and it is viewed as professional. That's why I nearly never go there. Even with AdBlock, it is dead slow to load and 99% of their ads are totally irrelevant to me.
Now, I also have a blog where I write about technical stuff I figure out and I have ONE AdSense on the page. I don't see that as a problem. What I really don't like is when a website takes 10 minutes to load a page because of the ads and then the content is spread out on 10 pages (10 pages x 10 minutes to load one article, no way I'll read that.)
Where I would NOT put any ads is on my company's website. There I really think that it would be stupid. That is, I will put information about my products and services, but no ads such as AdSense or those you pay may $200/mo. and I put your ad in the top-right corner... (which are often much more profitable, if you have enough monthly hits.)