In http://codex.wordpress.org/Forum_Welcome#Posting_Code is written "If you want to add more than a few lines of code to a post, [...]" and "[...] If you are posting just a few lines, [...]". But how much are "a few" lines of code?
It would be great to know that because it would save time and would help to resolve problems faster. Because if someone posts for instance 20 lines of code (e.g. in my opinion that are a few lines) and this code gets removed by a moderator with the advice to use a pastebin service instead, the one who has posted the code has to notices that the code is gone and needs to post it again. The recipient has to look again and this whole process may take some hours or a day more.
I think it would be a good idea to put a notice near the forum post editor box. Maybe below the notice Put code in between
backticks. Maybe something like: If you would like to post more than 3 lines of code at once, use a pastebin service and post here a link instead.