One of the most promising open source projects has to be Ubuntu. In a poll I put up a few days ago Ubuntu was the clear favorite, and the more I look at it and use it, the more I see why.
I've been watching development of Ubuntu 7.04 Feisty Fawn with interest and with each alpha release I'm seeing a platform that's getting faster, becoming more stable, smoother and easier to use. I'm finding myself saying things like "yeah, I can see ways to make use of this."
Here's a quick gallery I've put together which looks at Ubuntu 7.04 Feisty Fawn Herd 5, the latest alpha. I'm really looking forward to this hitting beta and then final release - it's got huge potential.
I'll have more to say about Feisty Fawn soon.