Chris McEvoy apparently felt that Google's simple interface was more difficult to use, because you had to click multiple times to find related Google services, like Google Maps or YouTube. Yahoo! offers a very crowded home page in comparison, but you are presented with most of your options from one page.
While that's somewhat mitigated with Google's new "Universal Search," it's still true to an extent. Google has been struggling with ways to present more options without making their home page too busy.
However, for every day Web searches, it's still easier and simpler to go straight to www.google.com and type your search in the box.
I think Simply Google is fantastic for finding new tools or exploring options you hadn't yet considered, but I wouldn't consider it to be easier to use than the standard Google home page for the average user. Simply Google is located on the Web at www.usabilityviews.com/simply_google.htm.