Brett1 wrote:is it worth upgrading to Leopard to use CO4? if so why, what is better?
Very briefly, the main pros of upgrading to CO4 are better image quality, faster processing and smaller preview files. The cons are that you need Leopard/Intel Mac (Snow Leopard will be released in about 2 month), learn new tricks (different interface), might miss some features (CO4 Pro though fairly stable is still maturing feature wise).
Main reason to upgrade however is that CO3 is end-of-life; no developments will be done towards the program. This means no new cameras will be supported, and no Snow Leopard support (it might work or not) in case you buy a new Mac in September or later.
You can upgrade for free if you have a CO3 license, and try it out without giving up CO3 (installs next to it; even runs parallel).