Stoyan Stefanov is all about the performance of web products. One small tool that gives you a bit of insight as to where you can optimize is a new bookmarklet he released today called statsy.
If you run statsy on a web site you get the following insights:

JS attributes (e.g. onclick) – this is the sum [...]

Wouldn’t it be nice to take a view of your application and see where the behaviour has been added? That is what is shown above, and it is courtesy of Allan Jardine and his new Visual Event tool.
Once you hover over an event, you get to see the code that will run:

Each type of event [...]