Opinions/advice on JavaScript libraries or write your own?

Hey All,

Ive been spending my spare time writing a web application, and have been using Dojo as my JavaScript Library. Ive done a fair bit of work on it including writing a bunch of custom widgets. Dojo is now up to v0.9. I use v0.4.3, and they are not compatible. Im very comfortable with the code, and don't mind branching off on my own version if requried.

What I am concerned about (especially after reading the "High-Performance JavaScript: Everything you've been taught is wrong" post) is the eventual speed, as it seems that some of the reason the Dojo guys are writing a new version is because of speed. ( I dont seem to have any issues with my app at the moment ... but still have a fair few things to add)

I guess my question is whether anyone here has completed an app in Dojo, or any other library, and whether you had to do alot of optimising afterwards?