Great post from former co-worker and sword wielding Dino-pirate, Corey, on Freshbooks shelving their old php based roll-your-own app and moving over to a web framework and new architecture. Core's the Chief Cat Herder over at Freshbooks back in the True North Strong and Free.
I particularly like his point on diminishing returns to adding new features and maintaining things that new web frameworks take for granted (ok, mostly because I agree with it ;-) )
We've actually taken almost exactly the same decision at GetUp! though we've decided to standardize on Rails and Ruby as our weapons of choice.
Anyhow, will be looking forward to seeing more posts on this subject. Would love to know of any gotchas they ran across in the transition.