I had a look at Kohana after your posts, and I really like the look of it, especially since I was leaning toward CI however didn't want to learn in an environment which was supporting a mix of PHP4 and 5. If I'm learning PHP now, I may as well learn PHP5 and work in an environment which can fully facilitate that without having to bloat up and lose flexibility by supporting 4 as well.

Kohana really does look like a great framework, however after reading the forums and wiki a little I'm worried that if I begin learning now, I'll need to change a lot of what I learn in the coming months with the 2.3/3.0 branch (whatever they end up calling it) - and whatever I start building will have to change too.

This isn't a huge problem as whatever I build now will be mainly side-projects which are designed to push my learning forward (such as small e-commerce sites, rating sites, file uploader sites), however considering the changes coming soon (API etc) it's a little frustrating.

However, thanks to you two I've found Kohana which is absolutely what I was looking for. Cake is a little too bloated and complex, CI is more flexible and simple, however to appeal to a larger userbase must support also PHP4 and 5, while Kohana is very niche insofar that is all about 5 and thus very much less restricted.

I'd be interested to see what other people who have worked around these frameworks think of Kohana.