Wave. Certainly there are things we've learnt from that, certain things we would have done differently," Mayer said without any hesitation (this one we're not really too surprised about). "Shutting down Dejanews.com at 11am on a Monday morning, and not having anywhere to post to or browse usergroups was perhaps a mistake," she also admitted (Dejanews was a discussion group website on the Usenet network which Google shutdown and silently archived to its Google Groups service). "Launching Gmail on April Fools day was widely misinterpreted," she added as a final thought (Google often "launches" ridiculous products on April Fools, so many thought Gmail was a joke until they realized it was still around the next day).
You can watch the whole interview below. The mistake question is asked 12 minutes in:
Interestingly, Mayer didn't mention anything about Google's various privacy issues. This is likely because the search giant has many related ongoing lawsuits, as well as settled ones, and it doesn't want any more press about privacy issues.