I used Blogads on my sites for several years, and have no complaints whatsoever about the experience. Their system works, their customer service is great, their commission isn't onerous. They're a good, solid advertising option.
I'm not going to tell you I didn't make money with Blogads, either. I did, and sometimes it was pretty good money, too! What it wasn't was consistent money. I might sell three ads one month, then none for three months after that, then one or two per month for a few months ... it was a crap shoot. A lot of the time, I contented myself with running ads for my own projects or giving friends "complimentary" ads for theirs.
That's not Blogads' fault, of course. If KN@PPSTER attracted a lot of traffic, it would probably attract a lot of advertisers, too -- and it would probably do so on a consistent basis. As it happens, however, KN@PPSTER greets a few hundred unique visitors a day on average, and a few thousand when there's an anomalous spike (e.g. when a popular site links to something here). Instapundit I am not.
After looking over various options, I decided to go with AdBrite. I've worked with them before and know that their checks actually come and actually clear ... and that they'll generate revenue for me consistently, even if at a lower level than an outfit like Blogads would if I could keep that strip full of purchased ads. People who really, really, really want to advertise specifically on KN@PPSTER can still do so ... but any unused space is filled in with "network ads" keyed in one way or another to the site's content, and I get paid per thousand views and per click.
If you run a high-traffic site which caters to an identifiable market niche, you can attract advertisers who are willing to pay a premium to reach that niche. In such a situation, I still highly recommend Blogads.
If your site or sites are of the low- to medium-traffic variety and/or aren't tightly keyed to advertiser-attractive market niches, I believe that you'll get more consistent revenue with a contextual ad service. AdBrite isn't the only one, of course, but if you're interested in them, well, of course they have a referral program: