The link to the Microsoft adCenter Labs Demonstration Keyword Forecast tool is allowed, though, as it's of general interest....
To follow up your question, the MSN tool does give (apparently) real numbers... and it's intriguing to play with. I'd tried it back when it came out, and I don't remember that it showed monthly impressions then.
For some searches I tried, the impression figures, compared with the Overture numbers, are much higher than I would expect for Microsoft's search volume. In some cases they're equal or higher than Overture's, and that doesn't make sense. I don't believe that demographic differences can account for the unexpected high numbers. So I don't know what to believe without playing with it more.
It seems very good at showing relative search frequencies among a few searches, and the graph is larger and shows more detail than Google Trends. It's got a nice checkbox feature that allows you to switch a phrase on or off... good for when a search is so much larger in magnitude than the others that it flattens all the curves.
Unfortunately, the input box seems to be limited to the number of characters you can enter, which makes this feature less useful than it might be.
As with Google Trends, many searches don't yet have any data. Taken with a grain of salt, can definitely be a helpful tool for comparing various searches... but I am thinking it perhaps overstates the number of impressions.
[edited by: mona at 8:45 pm (utc) on Mar. 12, 2007]