1. Make the list of favourite topics foldable. Have the one with the most recent additions on top and show only 10 of them, with the rest hidden by a show more-button. The way it is now, if you have subscribed to many topics, it takes a lot of scrolling each time you visit the forum to find the rest of the topics.
2. Increase the number of topics in the list of topics you participated in.
3. Add a preview function, so you can review your own post before actually posting it.
4. Disable auto-merging of your own posts. If I make a second reply right after the previous one, instead of editing the post, it is to reply to a completely different aspect discussed in the same topic, that I want to stand out on it's own.
Explanation: If a user ignores my post for the thing being discussed not relevant to him or her, his/her eyes should be drawn to the different post in which I discuss something else which may be relevant, not read the whole irrelevant post to find something relevant down in the post.
The merging function is especially grieving if you reply to a user that experienced something awful and want to comfort him and then adding a second post with a light-hearted joke on something completely different in the topic. The comforting words get merged with the irrelevant silliness. Happens to me too often in the bitch about life in general topic.
Some good ideas posted by others that I agree with:
4. Instead of a downrep-button, create a hide-button and a report-post button, with the report-button opening a field in which you have to explain why you report, which will be forwarded to the mods.
All great ideas, especially #4.