I had L4B4 up and running on a couple of machines this morning -- all seemed well when I got a balloon in the lower right offering me the opportunity to say how I wanted to handle updates. I said do it automatically, and since it showed 25mb ready, I said download
The icon on the systray then said their were L4 updates available and I clicked Ok -- that update went just fine.
I checked my Help | About screen (see atchd) and found that I'm still running L4B4, but it is a different release from the one I downloaded last night.