I hear about this PTC offers all the time and I really don't think it is worth the effort and time. IMO, it is better to invest time and dedication to other stuffs. The possbilities of earning online are endless. All you need is a solid idea and the passion to back it up
Affiliate marketing is also a good option.
You can make your own website or even just a blog. Get a lot of traffic into it and then monetize it thru a number of ways : PPC, Ad placements, sell text links, sponsorships, etc. Best that you drive in targetted traffic as this has the highest conversion rates.
A lot of big earners on the net started out with simple ideas and put their heart into it and eventually made it big