Think I figured it out - restart Impulse.
The sheer number of miniupdates today (at least 3 by my count, which might have something to do with the proxy servers coming online) were such that Impulse wasn't indicating when an update was available in the "My Games" list, so when I restarted my computer it notified me and I could update. I think restarting Impulse should be all that's necessary to make it show, so you can update and play.
Hope this helps you too!