If you updated OSX and find that jEdit no longer starts here’s how to fix it:
Make sure jEdit is not running!
1)control click the jEdit icon and choose “Show Package Contents”
2)In the contents folder you will find a file name Info.plist. Open it in text edit.
3)find the lines
<key>JVMVersion</key>
<string>1.5+</string>

and change them to
<key>JVMVersion</key>
<string>1.6+</string>

jEdit should start now but you may get an error concerning the OSX plugin. If you do go to:
Plugins->Plugin Manager->Manage
in jEdit and remove the OSX plugin everything should now work.

Here’s an update with a much better fix:
open the terminal and run the two following commands:

rm /Applications/jEdit.app/Contents/MacOS/jedit
cp /System/Library/Frameworks/JavaVM.framework/Resources/MacOS/JavaApplicationStub /Applications/jEdit.app/Contents/MacOS/jedit

Fix found here: http://ubergeek.tv/article.php?pid=144