It's truly unfortunate that I do have some experience with these types of sites, and yes you guessed it, they are mostly not worth your time. Some of them may just require that you run their 'special software' that will run in the background of your computer and make you money that way, but it may take you weeks or even months to generate even $5. One of my favourites was CashGopher, which I used for around two years, before finally accepting that it simply was not worth it considering that I had only made $20 in that time.
If you want my personal advice, I would say that if you want to make money passively, then it should be from you selling something without you always being there. For instance, it would be a great idea to create an E-book in a popular niche such as weight loss, and then post it to the Kindle store for people to purchase. Not only do you only have to do the work once (writing the ebook), but the passive income is unlimited as the ebook will never go out of stock, or be deleted if you follow the Kindle Guidelines.