I think the Alexa and Google Toolbar can be useful since they give useful statistics about websites, and allow people to use the search box built-in to it. Otherwise, I don't use toolbars most of the time.
Some toolbars these days made by AVG, Comodo, Yahoo, Google, and other trusted companies have security features to block pop-ups and scan websites for viruses or give warnings of fishy websites which mission is to scam uninformed visitors.