Guys, I've got some ideas to improve the basic functionality, which, as far as I've understood from various articles on the net, should be very much doable by means of AJAX. However, my own coding skills are not sufficient to craft these mods. Therefore, I'd like to share the ideas I have, and perhaps someone takes up the challenge to create the nifty mods to improve Snitz. They all are db-change-less, so no intensive modification of the basecode.
Idea 1: Username-check on registration page When a user tries to register, a username has to be chosen. When the user selects a username that's already in use, the user gets the error upon submitting the page. Instead of that, using AJAX, it should be doable to check the username that was filled in on the fly, and provide the user with a visible indication that the chosen username was already used.
Idea 2: Password-check on registration page Same as above, but now for the duplicate version of the password. If the two fields are not the same, show a visible indication that they do not match (for example by making the background color of the input field red or something like that.)

Idea 3: Subject check on post.asp
If a user posts a new message and forgets to enter the subject, he's prompted with a page telling him that. When he then clicks 'back' the message is gone. To prevent this from happening, we could disable the 'post' button as long as the subject isn't filled in. We could also change the backgroundcolor of the subject-input field to red.
Idea 4: Auto-update active topics count without refresh In the header, we can see the number of active topics. This number can be updated on the fly using AJAX, on a predefinable interval. For example 1 minute.<