Is it worth upgrading to CS3 from CS2?

Just for Bridge alone, and the Raw Converter.
and If you have an intel mac, another damm good reason

it does crash on my intel mac but never when I have been using it, bridge only ever crashed once, but CS3 photoshop does crash a lot, but it seems to crash when machine goes to sleep and I wake it up, I might add though never lost any work.

I went straight from PS6 to PS CS3 and I didn't notice any changes in the UI that I would consider a problem by any stretch of the imagination. The changes that I saw all were great improvements such as the docking and "icon-izing" of palettes to reduce clutter on the desktop. I was able to jump straight into CS3 without spending any time trying to learn a new UI. While doing some things the way that I did them in PS6, I am coming up to speed on all of the new features in CS3 and I have found them to be intuitive and easy to learn.

As René Damkot said, there are several features that make CS3 a very desirable upgrade ... I especially like the features of ACR 4.1. Whether it is worth spending the money is a personal decision that will not be the same for everyone.

completely?

it's not that different from CS2....

took about 30 minutes to get used to and find all that I needed

Ok, it has smart filters. What does this mean? It means, that in the same way you can have an adjustment layer for curves / levels, etc, which can be changed whenever you want, you can now do the same thing for things like sharpening, and other filters. This is a really useful feature. It has automatic alignment of images - do you have a couple of group photos where person a is blinking in the first, but three others blinking in the other? No problem, CS3 will align them, so you just have to rub out the area you want to show through - sure it's achievable in CS2, but it's more awkward.