For those who have upgraded to Internet Explorer 10 you might find a few issues such as the Enter key not creating a new line when you are typing out a post. This is a known bug which we are unfortunately stuck with until vBulletin release a fix.
However, as a workaround you can either:
1) Set Internet Explorer to run in Compatibility Mode for the SD site.
How to make Internet Explorer 10 run in compatibility mode
In step 3 select Browser Mode as Internet Explorer 9
2) Use the editor in non-WYSIWYG mode. When making your post press the A/A button in the top left hand side of the editor. This should allow Enter to work.