I have a slim as well. The update took a couple of minutes for me, and I haven't had a problem. If you still have it on. Pull the plug if it's not responding, then plug it back in and see if it turns back on.
You should call Sony tech support. Explain to them that after the update the system isn't responding. It's weird that some people are having problems after the update while others aren't. That could be the reason why they haven't released the update on their site. Touch the top of the system and see if it's hot, it may of over heated. If it is hot, give it an hour or so to cool down then try again, but regardless call Sony support.