Usually I try to devise comprehensive solutions, but there are plenty of smart people on HN - so I'll just give my perspective here:

When picking speakers, we typically look for three things: 1. Reach - what cool things have they done that'll make them interesting? 2. Popularity - how well known are they? 3. I they have reach and no popularity, will they be able to express what they've done in a way students will find awesome? Alexis Ohanian came to speak in CUTC 2011, and he was awesome, for example (although some would argue he was pretty famous too).

For #3, maybe something in terms of videos for each user in a centralized location

I know for the stage I ran at Agile 2012 we looked for things like:

* videos of speaking

* links to existing decks

* feedback on talks from twitter, speakerrate, etc.

If we couldn't get any of that I sometimes asked for a few minutes of video of them just pitching their talk idea. I know other stages at Agile 2012 did that to. The "video snippet" idea is one I've seen a few places. The folk who organise IxDA's Interaction conference have done it the last few years for example.