"At least 50% of people who have the toolbar installed are not technically savvy and a good portion of them probably didn't even intend to install the software (it was bundled with another download, etc)" - If you think this can't be possible, then you don't talk to enough normal people!
The thing that makes me say that a lot of people don't even realize this software is installed is due to two main scenarios:
1. When downloading other software, I have seen several instances where the Google toolbar is bundled, and you have to go into an advanced menu to de-select it.
2. Many OEMs are now shipping computers to people with the Google Toolbar installed.
I believe these two cases account for a large number of the installs. Possibly even greater than the number of users who intentionally go out and download it, but more likely in the 30% range of new installs.
Of course, I have no real numbers on this, and so it is pretty much a guess.
