Changing passwords

I just noticed that the default goautodial passwords were not very original.
First order of business is to change all of them, but I don't want to break something by accident... Is there any caveats I should be aware of before changing things like MySQL passwords?
First order of business is to change all of them, but I don't want to break something by accident... Is there any caveats I should be aware of before changing things like MySQL passwords?