First of all, credit where credit is due. This comes by way of @thinkontheclock via @josephfung (over a week ago). I spooled it, and just watched it tonight. If you've got 35 minutes, watch the first half of this talk. If you have less, I'll tell you where to start).
If you're a software developer of any kind, start at 10:20. If you see the GUI, and you're like "Yeah, that's nice, but how do I work with real code?" go to 16:25.
If you're an electrical engineer, start at 23:00.
If you're an artist, start at 29:20.
Don't wait if you can avoid it. Watch it now.
Bret Victor - Inventing on Principle from CUSEC on Vimeo.
If what you saw in those few minutes (of whatever segment you watched) impressed you, watch the first 35 minutes in its entirety. It's amazing, even if you don't exactly know what's going on every second.
If you want to see some of this in action, check out Bret's site, specifically the page on Tangle. (I'll forgive the hashbang URL this once, because you're awesome, Bret.)