These are the requirements/feature list of the previously mentioned rebuild I have so far, and some reasoning/notes

Comment Preview
There are a few ways to do this. i like the on-the-fly Javascript versions (e.g. //hicksdesign) and also the submitted form preview. The server method can help preven some of the comment spam, but the spammers will quickly figure this out
Search Hilite
A plugin that comes as standard with WordPress, that hilites search terms if the user was referred by a major search engine, or WP’s built in search
Remember Commenter
this is also an out-of-the-box WP feature. I like the way that it’s done at Binary Bonsai and Seriocomic
del.icio.us links
As I have already. I may get it converted to a WP plugin, or not.
Paged categories
The category pages get too long. I want to limit the number of posts per page. I haven’t found anybody that has done this already in WP, so it could be another plugin for me to do.
Live Search
Livesearch uses XMLHttpRequest to send search requests to the server and display result without having to load a new page. This one may not make it to the final version. I like the idea, but I haven’t thoroughly studied the downsides
Text Area Styling
I hate the default monospace font that textareas use
Comment validation
I believe that WP developers are working on this. It’s a nice to have, not a must have.
Some sort of Photo/Gallery interface
I want to build in a facility to easily upload and manage photos. Early thoughts are a plugin that works with flickr, but I may use Singapore
User Icons/Avatars
Like on Zooiblog
Noteworthy Comments
The ability to hilight noteworthy comments. Although I get so few that they are all noteworthy ;)
Related posts
I’ll do some more research, but I think there is already a WP plugin that does this
Spam filtering
There are a few different paths I could go down

Let me know if there are any other features that you would like to see.