are you referring to PPC sites like adwords or PTC sites like bux.to ?
PPC sites (like adwords) is a good advertising method but you need to have some experience in this field otherwise you'll end up paying lot more on clicks that what you make from those visitors.

Regarding to PTC sites...don't bother if you dont have an affiliate program or a money making related websites. Most of users are interested only in fast money making opportunities or most ofthem do not even read your site.. Just open the site ,wait for the timer and close it immediately.