How to improve camera shooting responsiveness? Is there a camera application (or other solution) that has quick response time between button press and taking the picture?  

On HTC Hero, the delay from button press to shutter is painfully long - focusing, etc seem to take a lot of time with the stock camera app.

On HTC EVO with the stock Camera app, distant shots focus and shoot quickly. However, closer shots can take some time focusing.
I think that if you tap on the screen to set a place for the focus, you'll gain some seconds for the effective shoot. 

It's also allow you to focus on a special part of the picture.

I hope it's help.