My experience, reggiecat, is that it gives me more time to be depressed. If you can allow yourself to put career management on hold for a bit, and regard your job as a stable source of income rather than something that is supposed to challenge and engage you -- just for a bit. Being under-utilized with a caring and supportive boss suggests that you may be able to put a fair amount of your energy into healing yourself.
Another option is to move to another job rather than simply quit. Starting the job search while you're still working is a little more difficult, but may give you a better feel for your state of mind and readiness to present yourself confidently and positively to others. If you find that you're not ready, you still have Plan A to fall back on.
Just my 2 cents -- everybody is different, and taking long-term disability could be the best thing for you.
Good luck.
