Google search term frequency

Is there any facility on the web that allows someone to find out the daily frequency of a particular search term in Google?

There are two reasons why this would be useful:

For AdWords customers, they could compare the number of ad impressions for a particular keyword against the number of times this keyword is actually entered in the search box;
(Of course, the value of this comparison is lessened if an AdWords customer applies country/language limitations to their ad impressions)

and

It would be useful for determining the maximum possible number of referrals from Google. Even if my site is no. 1 for all my keywords (which it isn't by any means), the maximum number of possible referrals is the number of times the keywords are entered on Google.

I suspect information like this is buried in a vault somewhere, but maybe someone knows something...

I just use the Overture Keyword Suggestion Tool -
http://inventory.overture.com/d/sea...tory/suggestion

and I make the assumption that there cannot be a huge difference, PROPORTIONALLY, between Overture and Google.

Can anyone suggest a reason why statistically, they shouldn't both show the same relative keyword rank?

In other words, if a keyword is frequently searched for on Overture, wouldn't it also be frequently searched for on Google?

Thanks for that suggestion Surf-Dude - it certainly does help.

I read previously that Google has 70% of all search activity, so I must find out the percentage currently held by Yahoo to work out the proportional calculations. Is it fair to assume that Yahoo has about 25%?

I just did a quick check of 2 of my sites -

62% - 63% Google
20% - 19% Yahoo
11% - 10% MSN

Remarkably consistent between the 2 sites, which are very different sites - one retail and one informational.

Hope this helps.