When viewing the main questions page, questions have their tags listed below them. Currently, when you hover the mouse over a tag, a tooltip comes up with information on the follower count, some options and if given a tag wiki summary. It would be useful to be able to determine immediately just how many questions are tagged with that tag; I propose altering the tooltip to read something like "view 23 questions with the TAGNAME tag"; that is, to add the number of instances of that tag to the tooltip for the tag.
This would be useful to be able to view the relative popularity of the tag without needing to traverse any links, and should be relatively technically simple to implement; tag tooltip text could be cached and updated occasionally to obviate the need to query the DB for the number of tags on each pageload.