In many ways the Canon EOS 5D is very similar to the Canon EOS 30D. There are some very substantial differences - the most notable being the fact that the 5D has a full-frame sensor and doesn't apply a 1.6x magnification to all my lenses. Two other inconveniences (differences that I'll have to adapt to) are the lower maximum-frame burst speed and the increased weight.
After two hours of continuous, on-the-go shooting with the 5D I found the muscle between my thumb and forefinger to be strained (I have small hands). A fellow shooter recommended getting the battery grip (I'd initially assumed that it was just for the ability to shoot longer without recharging). My next shoot will be with the battery grip (which just arrived from BH Photo, I also got one for my 30D) so I'll see if that helps.
The 5D is much more forgiving than the 30D (12.8 Megapixels compared to 8.2 Megapixels) giving me a lot of data to work with in post-processing (not that I've actually had to yet). The CR2 files from the 5D are truer to my vision than the CR2 files from the 30D with default Adobe Camera Raw (ACR) settings (there are separate defaults for the 5D and for the 30D). Not having to verify camera settings (EV biases) for the images in DPP and then reset them in ACR saves so much time. The LCD for the 5D also appears to be a better representation of what is indeed being captured. The LCDs for both of my 30Ds show the image lighter than it ends up being in ACR (as bias corrections don't flow through to ACR I haven't found an easy fix yet).
So far in spite of my sore hands, I absolutely love my 5D.
