UPDATE 9/5/10 - Now another game is available in the pack, Samorost 2
Taken from the website:
The Humble Indie Bundle is a unique kind of bundle that we are trying out.
Pay what you want. If you bought these five games separately, it would cost around $80 but we're letting you set the price!
All of the games work great on Mac, Windows, and Linux. We didn't want to leave anyone out.
There is no middle-man. You can rest assured that 100% of your purchase goes directly to the developers and non-profits as you specify (minus credit card fees).
We don't use DRM. When you buy these games, they are yours. Feel free to play them without an internet connection, back them up, and install them on all of your Macs and PCs freely.
Your contribution supports the amazing Child's Play charity and Electronic Frontier Foundation. By default, the amount is split equally between the seven participants (including Child's Play and EFF), but you can tweak the split any way you'd like.
Rep would be much appreciated :)