I'm glad that iPhoto supports RAW now, and I'm glad that people are beginnng to take digital photo processing seriously, but I'd hate for people to get the wrong idea and start thinking that RAW is necessarily better than JPEG all the time.
It really depends on your camera more than anything else whether or not you actually want to use RAW. Furthermore, if you're going to be playing with RAW files, you really should get a better photo editor than iPhoto.
All RAW really is is the direct output from a camera's CCD. It's the image before the camera's internal firmware gets a chance to process it. For some photographers, this is a good thing because a few minutes in Photoshop can create much better images from the RAW output than the camera's chintzy little firmware can.
So if you're shooting with say a Konica Minolta DiMage Z2, then you're better off using RAW files because the camera's internal image processor has a strong tendency to create lots of noise and compression artifacts. But if you're shooting with an Olympus C8080WZ, you really should just shoot in JPEG mode because that camera's internal firmware does an amazing job producing great looking pictures in even the toughest lighting conditions. In order for you to take the RAW image into Photoshop (or iPhoto) and do as good a job as the camera does on its own, you would have to spend a significant amount of your time tweaking it.
RAW support is a really great thing and for professional photographers or really serious hobbyists it allows you to take some great pictures that otherwise would be troublesome with most digital cameras. That being said, sometimes you really are better off just using high quality JPEG compression in the camera's firmware and if you really want to take advantage of all that RAW has to offer, you're going to need a stronger tool than iPhoto.
At most the RAW support in iPhoto means that hobbyists can now catalog their RAW files along with all of the other images they catalog in iPhoto which makes it more convenient to use and organize their photo collections. But anyone who was using RAW files before this iPhoto update already has Photoshop or Photoshop Elements, both of which are much better for editing RAW and for importing RAW files from your camera.