"immediate and reliable" is a great way of putting it. It's instant, guaranteed traffic. The quality of the traffic is based on your ad copy and keyword research. If you are a local company you can target your ads to geographic locations.
We started with AdWords when it first came out in 2002(?) as we were already using Goto.com (Overture, Yahoo & now MSN).
It was an instant success for our B&B business. It has been increasingly difficult to maintain a full program with them in the last 18 months because of high first page pricing. We are now using more TripAdvisor/FlipKey & less Google however we can't really be without.
I used to sell YP advertising (13 years) in the Ontario market prior to 1987. It was a great product then (& I made loads of money) however I assume the printed issue is like the buggy whip industry now.
After living in South America for more than 20 years I have lost all touch with what's happening up there now.