I've been using Atahualpa on a page since about March, but Tuesday was the first day we received significant traffic. Things went down in a majorly bad way and I need advice on what part Atahualpa plays and whether it will scale for this level of traffic in the future.

A post was linked by BoingBoing, we got 25,000 views that day and our server was brought to its knees within the first hour of the posting. We're on a shared server, but our hosting is tended by a real pro. Query numbers were unnecessarily high. We disabled all plugins except Akismet, WP Spamfree and WP Super Cache. Queries were still abnormally high. As a last resort, we changed the theme to the default WP theme. This settled things and they've run smoothly as we weathered the storm.

I would love to get feedback from anyone using Atahualpa on a site that gets Slashdot or Digg-like spikes in traffic at times. How has it worked at this level?

It might be an idea to check out how many sites are hosted by the server you share. Regardless of whether one technology will scale well or not, nothing scales well on shared hosting. Wordpress is not well known for being a resourse friendly cms.