You're probably thinking, "I'm already using iPhoto, so what's the big deal?" That was certainly my first thought too, but then I downloaded the software to test it out, and I changed my tune a bit. Picasa for Mac pulls in images and videos stored anywhere on your hard drive, lets you edit and tweak, save changes, and of course upload them to Picasa.
Picasa for Mac, which is still a Google Labs application (meaning it's not perfect), has a feature set that is pretty darn extensive — it would be almost impossible to list them all — but some cool things you might like include the ability to filter by stared images, images with faces, and movies. You can also batch edit photos, create collages and movie clips, publish to Blogger, take video snapshots, one-click upload to YouTube, and a whole lot more.
And even if you're not ready to chuck iPhoto out the window (I know I'm certainly not), you can still use both tools side by side. In fact, Picasa for Mac lets you run both applications without overwriting changes to your iPhoto library. iPhoto library images, within the Picasa software, are treated as read-only, so any photo adjustments will create a separate copy of the original image.
For more information on Picasa for Mac, watch this short video provided by Google:
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