Others say...

"Big Difference"
I was going to skip CS3 (since I have CS2) and wait for the next version they come out with, but I just recently bought an Imac and decided to download the trial version of CS3 (with intentions of transitioning my CS2 licence from PC to mac) but the new ACR and Bridge are so much better, I decided to buy it and keep my CS2 version for my backup PC. Adobe Raw Converter is now functional enough that once you make your edits and save as .tif & you are done with it. I usually made some changes in ACR (on CS2) saved and then tweaked the .tifs again to get my images where I wanted them. Sometimes, I do very slight changes and the image really blossums into a beautiful photograph. I have only had this for a couple of weeks and am still learning about the differences so I am a little premature in my ability to cover all of its capabilities, but I will say that what I see so far is very impressive. Adobe Bridge is also easier to work with and I like the new layout of it as well.

"A huge step up from Elements"
I had a hard time convincing myself to shell out over $600 for this product. I downloaded the 30 day trial and worked with it for a few days, but the price was still a sticking point for me. So I decided if it ever went below $600 I would buy it, and fortunately Amazon put it on sale for a couple of days for $585. I took the leap and am glad I did. Now that I have worked with it seriously for about a week the performance gains from native Intel support and automation of workflows has made me very productive. Keep an eye out for occasional deals, they will pop up.

"Much Faster than PS2 with Intel Processors"
I am a profesional photographer. I often work in photoshop with very large (200-300 MB) files. I use a new Imac with the new intel processor. With CS2 there was considerable lag time with many of the applications when working on the large files. With CS3 the lag time has been eliminated. All the applications are almost Instantaneous. To me this is the single most important improvement in PS3.

Other improvements that are very useful to me are, a significantly improved Camera Raw dialogue, improved Curves dialogue with histogram, an improved Bridge. In all I feel that PS3 is well worth the money for profesional or serious amature photographers, particuarly if your running an intel processor.

"Much better than Photoshop on a PC"
After years of struggling with various versions of Photoshop on a PC, I finally got to experience Photoshop on a Mac (just an Intel Mac Mini, nothing terribly high end). What a difference! Even though the UI is just about the same as on a PC, Photoshop works much better on a Mac. Hard to explain why, but perhaps no explanation is needed.

"Using Photoshop CS3 Classroom in a Book"
For those of us using the Intel Mac platform, CS3 is a long awaited program. Now that we have it, let no one tell you Photoshop isn't the most difficult program you will ever use. Photoshop is probably the most documented program out there in terms of "learning and using" tools, texts and tutorial sites. If you're new to Photoshop, get ready to get your hands really dirty and your mind in a real state of, "something." Join the thousands of users who need help!
I come to Photoshop CS3 having used several versions of Elements over the past many years. In this respect, I am quite fortunate that I am not starting from scratch. But CS3 is a whole new world. Adobe Photoshop CS3 Classroom in a Book is probably a good starting point for many. The key to the book is the included CD which contains everything you'll need to work through the detailed lessons. And believe me, the lessons scratch everything you'll need to understand what you've gotten yourself into with Photoshop.
Initially, I tried to use the book and CD as a "resource" building on what I knew from using Elements. This really doesn't work because the book isn't constructed that way. You just have to grit your teeth and "follow along and do" what's going on in the book using the included images, etc. Although you can use your own images to do the extensive lessons, I wouldn't recommend that approach. The included images are designed, first and foremost, to allow you to do what's being done in the lessons. If you attempt to use your own images ( and I did ) you set yourself up for frustration. While the particular tool or process you are learning will eventually be carried over to your own work, your image may not be as easy to use because of tonal differences or backgrounds which may "confuse" the tool you are using. Just bite the bullet and "do it by the book!"
Although the book appears to target new users, experienced Photoshop gurus can learn particularly when it comes to the many new tools and features in CS3. What's my overall opinion? On balance, this is not the best book for me. I have just enough knowledge to be dangerous! I prefer to learn by doing -- right or wrong. I prefer to "try this and that" although this method can be frustrating. I also prefer to learn by using specific tutorials designed to do what I am trying to accomplish. I beat the seemingly endless video and written tutorials available to NAPP members ( you probably better join! ) until they are worn out. Depending on your knowledge level and learning style, this book may be either "perfect" or "something else." I am neutral on the book. What I am really waiting for is Scott Kelby's forthcoming book on CS3 because, if his history is any guide, it will be a super learning tool.