Alexa Toolbar use in the US has decline from 36.91% last year to 14.28% as of now. In fact according to the Alexa Blog it’s losing users in just about every country except Taiwan. The reasons range from users getting Firefox and using the Search Status Toolbar to it’s privacy concerns.

seonewsblog.com/alexa-toolbar- ...

Thank You

Well, that's somewhat inaccurate. They aren't losing users, it is just the share of US users is being diluted by international users. Money quote:

"While we have as many U.S. users as ever, on a strict percentage basis, they are declining as the Alexa Toolbar grows in popularity across the globe."

Which is straight from the source: awis.blogspot.com/2007/02/alex ...