In this WordCamp San Francisco 2011 presentation, Sheri Bigelow talks about the "Top
10 12 Features You Aren’t Using – But Should Be!" (27:24).
This is an excellent presentation for new WordPress users, but it includes a few things that WordPress veterans may not know about, like the Post Revisions Easter egg at 18:30.
The travel funds aren't always available to go to conferences, but at least most of the sessions from the regional and national WordPress conferences (aka WordCamps) are posted online. I will occasionally repost some of the germane ones here. Presentation slides are after the break.
The first four minutes do not apply to a multisite blog, so you can skip ahead.
In this first one, Hanni Ross from Automattic talks about the "Top 5 Ways to Break Your Blog – and Fix It" (21:32)