In general I think people don't want to say too much about what they make, unless they aren't making much. When I started out, I parked about 30 domains at SEDO. after a few months I found I had made: a few dollars. My friend gave me a lot of good advice and one thing he said was to try a provider for a few months and if you have some domains that don't earn, move those to another provider and try again. Avoid parking providers that have a history of closing user accounts without notice or a valie reason.
Revenue per click varies greatly from provider to provider and of course all the different keyword ads that are displayed. It can range from one cent or perhaps even less, to several dollars. One of my friends has a domain at a service and told me the most he ever got for one click was about $28. For me, I think the most was about $7. Most of mine are under $2, which is the most per click I have ever seen on my sites with AdSense.
You are correct that the idea with non-premium domains is to get enough traffic voulme, or high enough $ per click to at least earn the reg fee in a year. Like most businesses you want to at least "break even".
You want to get the best names you can, and all those starting out should spend a lot of time on the forums learning BEFORE starting to buy domains. If you don't, you may have domains you think are good, but that aren't really. And it can sometimes be hard to sell those domains for $5 when you thought you were going to strike it rich, or worse, you fall in love with that dog of a domain, and keep renewing it because you have personal feelings for it. There's nothing really wrong with that, but you should be honest, admit you have a problem, and seek professional help...!
One thing I have to tell you is that it IS possible to make money with domains that most experts will tell you "suck", but you need to know what the heck you are doing. My top 3 domains this month so far are .cn domains. In the top 10 I also have 1 .in; 1 .us; 3 .info; and 1 .net (and it has 3 words and 2 hyphens). The highest one so far this month has earned $93.08 so far. The 10th one on the list is at $20.29. Out of my 1,035 domains, 390 have earned more than $0 (some are less than one cent) with the rest having not earned anything this month.
The traffic and income from low-traffic domains is inconsistant, and so are the clicks from what traffic you do get. I have previews of what my traffic is and see an estimate on what I'm earning, but if you get non-US traffic it may be invalid. I can't predict very well what I will earn from day to day, but in general if I get more traffic, I earn more money.
If you park someplace where you can optimize your domains, there is a good chance that the search engines may find them and index them, otherwise you are limited to type-in traffic.
Those of us without the money to invest in valuable domains, like ones with single keywords that get type in traffic, have to make do with finding rare ones that WILL get some type-in traffic, have traffic from links because they used to be a site on the domain, or we optimize and promote the domain just as we would any web site.
Some providers may permit you to pay for advertising to get traffic to you domain, but as was mentioned above, most parking providers DO NOT ALLOW you to do anything to get links or traffic to your parked domains. However, some of the parking services DO allow this. I think Domain Spa is still one that does. But if you are thinking about promoting any parked domains you MUST check with the provider first or they WILL close your account if you break the rules found in their Terms of Service (TOS).
