How about adding a catch into the submit new question code that checks if that user has posted another question under the same topic in the last .. errr.. 10min (timing can be adjusted) and if they have give them the option of "do you really want to post this as a new question" or "do you want to post this as an update on your previous (question title) post"
In theory it's a good idea... but those that like to do this sort of thing are just going to go ahead and post anyway Chuckles. Not that I'm a cynic or anything you understand.
Yes, could be an addition as a preview feature. In ym mind the preview would have the following:
* Display the content as it would be seen on site
* Display related questions
* Display your most recent questions (this might get to the bottom of your issue?)
I'm not sure if it would work under the same topic as those who repost tend to cross-post across categories?
I like the Disqus.com forums that a lot of different sites use. After you have posted and seen the glaring typo, it lets you edit your post. I prefer that to the preview method.