for your exact upgrade window)
New today - and just in time - is our Release Readiness Live Bitesize playlist on YouTube where you can go directly to the feature you're interested in so skip straight to Process Builder, Sales Cloud enhancements - that's where Sales Path is hiding - or whatever interests you most.
If you've been meaning to get up to speed on Spring '15 but haven't had the chance, start off with
@Elna Miller's Goodie List at http://sforce.co/1Knlygl for the best roundup of all the blogs and resources available to get you ready.