Normally I'd be a bit skeptical, but these guys are supported by the SFWA and Electronic Frontier Foundation (both of whom would receive funds from any purchases you make), so they seem legit. Also, it seems they've been doing this for a while, though not necessarily for ebooks.
For the next 14 days, the bundle includes ebooks by John Scalzi, Neil Gaiman, Lauren Beukes, Mercedes Lackey, Cory Doctorow and others.
UPDATE: Here's the LA Times:
BoingBoing tells us that Humble Bundle has previously raised more than $7.2 million for charity. That must be because of the genius interface, which is far more transparent than those of most charitable operations. The site has a live online ticker showing how many bundles have been sold, how much money has been contributed and who the biggest contributors are.
Want to give more than Wil Wheaton (or someone making a donation under Wil Wheaton's name)? Then pony up more than $242.
The offer, which went up Tuesday, will continue for two more weeks. When I began writing this post, about 10,000 Humble e-book Bundles had been sold, and the number has been steadily climbing. Funds have exceeded $150,000.
And here's some wikipedia background.
Still a bit at a loss as to how it works--I mean, how do they actually get the titles? Are publishers compensated? Etc. Educate me in the comments, if you like. Or on twitter: @nerds_feather