Here's an idea: What about a default message in the text area when you open a new topic?
Describe the problem in detail. Be as specific and detailed as possible about what you expect to happen and what actually happens. Don't forget to surround any code samples with [code]...[/code] tags. This highlights your code and preserves its indentation, making it easier for people to read, which in turn increases the chance of someone helping you with your problem.
The message text would be highlighted by default, so as soon as you start typing the browser will automatically delete its contents. Some people might actually read it though.
The problem with automatically detecting code when the user's post count is low is that once their post count goes over the limit and the code tags aren't automatically added any more, they won't understand why their code isn't being formatted because they won't have learned.
It's much better to put some obvious text. I think the reason most people don't bother with code tags is because they haven't spent the time to look at the stickied posts. If the example text is right where they're intending to write their post... at least some people would read it. The others don't deserve to be helped in the first place.
That does look like a good idea (I missed this post when it first appeared).
Maybe augmented with an additional, brief comment?
PS Of course, we need to provide our e-mail addresses to cplusplus.com when we register, so we could get the server to analyze all new posts and spam anyone who is naughty until they come back and tidy up! >:->