ALWAYS unreliable, but useful to throw the competition off the scent of the real value keywords.
It's when you get a bunch of keywords and let's say you bid 20p for all of them and it suggests you'll get 50 clicks a day, so you increase the price to 30p and it says you'll get 40 clicks, so you reduce it back to 20p and it says you'll get 60 clicks, so you reduce it to 10p and then you will get 70 clicks.......
For a while Web Diversity I thought I was the only one. I would just watch ADwords like a hawk, because as you suggested you never knew what to expect. This is why I am amazed at the bashing of Overture, and the support of the new ADwords content ads. Google is building new services on top of an ADwords program that is VERY VERY difficult to interpret. I go back again to something I have said several times-speed/flexibility/low quality control/lack of information on bidding (bidders) vs. slow/inflexible/high level of quality control/and full disclosure.
It is indeed difficult to know what to expect with Adwords.
If I were to advertise on the prime time TV show "Friends" and pay a premium for it, the television industry would not automatically show my ad on "Barney and Friends"! I think that aspect of adwords is absolutely rediculous. Google should be the king of 'relevancy' and they miss the boat in this respect with adwords.
Overture's system is a little more to set up, but well worth the effort of putting in specifics.