This question already has an answer here:
I'd find it useful if the number of items to review (say, the total number that your permissions allow) could display in the main menu bar next to the review link, similar to how your reputation and number of badges show up net to your profile link.
The reason I ask is because it is a little annoying to keep checking, only to find that there are zero items to review.
But I do understand if the volatility makes it infeasible to keep it on every page (those posts that are there always go so quickly!).
I think I've seen this in the new top-bar - status-completed?