What we should have is an implementation whereby every journal entry is a new topic, and then comments are replies to that topic. Switching to this will not only be a performance win, but it will be a functionality win as well - some things are simply impossible to support under the current journal implementation (for example, closing comments on a single entry), while other things are needlessly duplicated (for example, RSS feeds - if a journal is just a collection of thread-first-posts, we can reuse the RSS we've got for providing feeds of a forum).
There are also other changes I want to make with regards to the way journals are actually retrieved and rendered - to the extent that I'm basically rewriting them from scratch, using tasty things like XML queries and XSLT to make it clean and fast.
One of the things I can change is the way the right-side bar is rendered. I'm not massively happy with the way the bar looks on journals currently; the calendar isn't particularly useful, the RSS button is obsolete, and the monthly links are just run together into a single unstructured list. You can see my proposed replacement here.
The biggest thing I'm not sure about is whether people will be upset by me dropping the Calendar. I think it's fairly useless, but I know some people enjoy making little patterns on it and so on. Implementing it will take a fair bit of work - there's a whole extra DB table that appears to be dedicated to it - so if I can get away without it then I'd quite like to, but what do you think?