tedster - 7:41 pm on Feb 21, 2011 (gmt 0)

Last I tested this, it seemed that alt attributes were not as strongly scored as visible anchor text - but they were definitely used in the scoring. In fact, more recently SEOmoz published some correlation studies that showed alt text has a very high correlation value with ranking well. That's correlation, not causation, but the evidence was convincing enough for me to make sure there's a real alt attribute at least in the page's "hero" image.