Oracle SQLDeveloper locks up when using copy/paste
Solution 1:
There could be lots of problems here:
First, that is an old, old version - any chance you can upgrade to at least 1.5, or even better give the 2.1 RC a shot?
Second, as this is a java app - what VM is it using? In my experience SQL Developer is one of the most picky java apps I have used about what VM it runs on or has issues with. I would recommend grabbing one of their builds that includes a VM just to see if the problem goes away.
Third, are you pasting rich text by chance? Try pasting in from Notepad or something similar to make sure it is just plain text on the clipboard. I have seen many applications struggle to convert between RTF/HTML and whatever they use natively and hang up as they attempt to process the information on the clipboard.