@ryuken
You can't generalize like that
there are many ptc sites where you have to see the advertisements even if you switch on another tab the timer gets stopped
also,in some ptc's timer doesn't start till the whole page is loaded,so that means traffic
So you have select ptc's which has such features..

Well it all depends what kinda site your trying to get traffic too.

The best way i find to get traffic is to promote it in forums, by adding your url in your sig to help promote it.
Buy or Get Free links to your site, to help get more backlinks to your site.
Submit to Directorys.
Make a contest to help bring in the traffic or give a few things away Free.
This is jut a few things to help ya.

And also you can buy some softwares available in markets, i heard which will increase your traffic like rapidly,so try that so that you can earn lot through your site,it really works for many.