Rated 2 out of 5 stars

Pros:
Nice clear display in Firefox of the owner of each link (when known).
Works reasonably well but ......

Cons:
Causes Firefox to hang when clicking certain links.
Causes Firefox to hang closing tabs.
Sometimes Firefox will load & shut down immediately.
Reports some sites at risk which are trustworthy. (see ben101 review for full reason)
Poor support.
Reported discrepancies are not rectified.

Summary:
Had been wondering for some time why Firefox kept locking up when clicking certain links. Had to change the configuration settings so that links that opened in a new window opened in a new tab instead. Worked for that problem but then closing a tab for some sites would lock up Firefox completely and the last straw came when I upgraded to Firefox 3.0.10 and clicked the link within Firefox's own site to see the 'list of bug fixes' and Firefox hung yet again.
Disabling all the Add Ons and then enabling them one by one tracked the culprit to Callind ID.
I have now permanently removed CallingID from my system and all works well now with just Site Advisor (version 26.6 I hasten to add).
Also I contacted support about why some sites have a question mark but then clicking the link says the site is verified. This problem has never been resolved and my last email was completely ignored.
There was a form to fill in at the end of the un-installation process which asks why you uninstalled. Sending the form returned an error.