I am currently in Australia (catching up with family and warming up from Maine weather)...and I have some time to write down some notes on collecting rainwater and the things you might need to consider:
Is it legal
Is it clean
How can I store it
How do i get pressure
Bottom line, its worth it! You can save money if you set up a system to replace town water, and if it is your MAIN water supply, you need to know how to make it safe and effective....
I live in Maine...we have too much water most of the year. I never have had to water almost anything. However when we lived in Colorado, we needed to water plants (trees, veges) a few times a week and even a day in very hot spells. And in Colorado...we did not own the rain that fell on our farm..!!!