That really depends on how much time and money you spend, and what kind of ROI you expect. Adsense is probably not the most profitable way to monetize all sites; affiliate marketing may be better for you.
Majority of folks earn little from Adsense, you'll need a good niche forum, like DP to generate something worthwhile... and getting a forum off the ground takes work...
I dont really create adsense sites but i add adsense to sites where it makes sense to, and i feel its worth it.
Would be nice to know how much % of adsense publishers consistently earn over $100 per month. My guess is well under 10%
It all depends - what the OP meant by "adsense revenue generating site" Since there are millions and millions of "adsense revenue generating sites" on the Internet, then by that definition, yes of course it is profitable for the millions of webmasters.
I've got 2 sites which each earn, on average, $85 each per month. I don't even promote them; so it's quite possible, and not that hard to do.
When I was writing articles for backlinks it took a lot of time, but cheap 3 way links makes my hourly rate much much higher...