There are many true PTC sites (I tend to classify FC and Inbox Dollars as a GPT (Get Paid To) site instead of PTC (Paid To Click) since there are many different ways to make money on these sites instead of just clicking on ads, as you do with true PTC sites like Neobux or Clix Sense) that are not necessarily scams, but take a very long time to make any meaningful money with them, esp. if you don't want to spend any of your own money to do so.
Although I wouldn't necessarily call Neobux a scam since they do pay, as OldBuddy mentioned above a few years ago Neobux had drastically changed their pay rates for clicking on ads, while at the same time keeping their expenses (at least for renting referrals, upgrading memberships, etc.) the same. When they had first started, each click was worth 1-cent for standard ads, even for their free members, and they guaranteed 4 ads per day for those free members; but after the change, the values dropped to a 1/10-cent -- a 10-fold decrease in earnings. I know I lost a bunch of money when they did that... Many of my referrals saw that they weren't making nearly the amount that they had before, so they stopped clicking. Recycling didn't help much either, since 1) the cost to recycle was still the same price and 2) the "new" ones I got usually were just more unsatisfied members that dropped shortly after they made their change. Plus just before that, they had instituted a change which tacked on a fee if you let a rented referral expire. I had closed that account shortly after that change over, but last year I opened a new one to see if I could make money on it... Although I have been able to cash out a few dollars from it, I haven't made much on it esp. if you consider the amount that I've earned from FC in the same amount of time.
Also for any PTC sites that offer rented referrals, you have to spend a little extra time maintaining those referrals in order to make sure that they are making money for you. For example with Neobux, a standard member gets 1/2-cent per standard (and fixed-ad) clicks and cost 20-cents for 30-days. Thus those referrals need to average 1 and 1/3 clicks per day to break even and even more if you decide to "recycle" or change the referral that you have rented, since it costs 7-cents to recycle a referral. And in order for you to earn from these rented referrals, you need to click all of your fixed ads from the day before, so if you skip a day clicking ads, you also lose all of those referral clicks for the next day as well. So like for me, I tend to do less on-line stuff over the weekend, so I usually miss out on referral earnings twice a week.
I think if you are looking at pure PTC sites, Clix Sense is probably the best. Their upgraded membership costs less than $20 (compared with $90 for Neobux's cheapest upgrade), the click-values have a better average (I tend to earn between 10-15 cents per day with my own clicks and even closer to 20-25 cents if I'm very lucky vs. maybe 5 cents average on Neobux with 10 cents if I'm very lucky). Also on Clix Sense, you can earn down several levels from your referrals if they upgrade (eg if your referral has a referral of their own, you can earn from that 2nd level referral as well down thru 8 tiers of referrals whenever any of them upgrade their membership).
Probably the best way to earn money on these sites it NOT thru their method of getting money from clicking on ads, but rather by creating ads for yourself for some other product / site. For example, if you are making some pretty good money on your own thru FC, you may want to sign up on some other PTC site to advertise your own site / blog explaining how great FC is and providing your referral link for them to sign up under. I know many marketers will take their earnings from, say, Clix Sense and instead of cashing out, will use that money on advertising credits for their other site, esp. if the Return On Investment (ROI) for that other site is greater than what it costs to advertise. Also, if you create your own site / blog that describes how they can earn money, show proof of what you've made, and provide an e-mail for additional support, people are more willing to join under you knowing that they'll have that additional help in getting them started on making money on-line.
For comparison (in my own experience, counting only my own actions (eg no referral earnings)) I can make close to $100 per year with FC, $20-$30 with Clix Sense (being an upgraded member, after factoring in the cost of membership), and only about $5 with Neobux (standard membership since I seriously doubt I'd even come close to covering the expense of a Golden membership on my own).