There seems like there's 3 different categories of making money on-line:
1) Scams. These include ponzi schemes, matricies, cash gifting, or even the $40 e-book that tells you how you can turn $100 into millions. Although they may be considered scams, you could feasibly make money, as long as you know it is a scam. Think of them more like a gambling game... You know the odds are stacked against you, but as long as you just play with money you are willing to lose, do a little research, and don't put all of you eggs in one basket, you can make money. I had tried a High Yield Investment fund investing $5 that I had earned from some other sites. I would've gotten that money back had I not been trying to use the money to reinvest in the account. But then they claimed they were scammed by a bunch of people using AlertPay and closed their AP accounts and zeroed everyone's accounts to pay off what they owed to people awaiting payouts via AP.
2) Tasks / Jobs. These include legit surveys, GPT sites like FC, PTC sites, reading e-mails, article ratings, and "Mechanical Turks" type of tasks (MTurks is through Amazon). These are very simple tasks / jobs that take only a few minutes to perform and where you can earn fractions of a cent up to a few dollars per task. These are things that anyone can do (although in the case of surveys, not everyone can do all available, only those you qualify for). If you were to just do these tasks on your own, you won't be able to make a living off of it. But many will offer some type of bonuses for ref's, and they usually are so quick and easy that you can pick up a few cents during your free time (like doing surveys during the ads while watching TV). This is how I get most of my money on-line. I'm involved with several survey sites, FC and some other GPT sites, and a few PTC sites (although I've lost more money with these because I tried going too fast all at once and used my own money for investment instead of learning how to reinvest like dkanofsky said).
3) Work / Careers. These are for the heavy hitters that are willing to put in the effort and treat it more like a true "brick and morter" type of career. These include product marketing (including affiliate marketing as well as marketing your own products), blogging, medical transcriptionists, programming, article editting, etc. Most of these jobs require more training and/or education in order to be successful (although experience can also work, but it just means a more difficult line to tow). And they also require dedication, esp. in the beginning when you are first trying to set yourself up. Me thinks OldBuddy is working more at this level, and someday I hope to do so as well. I'm thinking of having two different blog sites: one would strictly be for making money on-line in order to get more ref's for the sites I like, and the second is more of my own personal blog sharing my own ideas / feelings, where I'd use affiliate marketing and AdSense, etc. in order to make money.