it might scare away some users. also some ad providers don't provide proper checking of what content they serve, so if you chose to serve ads, be a bit picky with the ad companies that you can use to do so as malicious scripts comming of your blog will definatly scare people away.... on the other hand, i do support people making a little earning of their blogs, so i don't use ad block, where a lot of people will be indifferent to your decision as their ad block will take care of things.<p>I would say in the end it doesn't really matter what you pick, though if you think it's a nice little extra at the end of month or year, why not :) little compensation for your efforts / sharing doesn't hurt!<p>(some pages just slap some adds in the footer or so, so the main content is always displayed first, and the user doesn't have to dodge ads anywhere on the page if they want to click stuff..).
Another alternative you might consider is an affiliate program, ads can and most likely will be blocked by an ad blocker and even if they're not you won't make that much anyway, but an affiliate banner you put on your site won't be blocked and might drive some revenue.