If you can confidently assert that every shell script your system runs is "decent", then you'll have no problem. The thing is, very few of us can confidently make that assertion.
That all depends where your shell scripts come from.
In my experience most of the shell scripts provided by packages for debian, do use /bin/sh.
A quick check of .sh files on a couple of squeeze/wheezy installs showed that the vast majority of shell scripts using Bash come from node modules, which quite frankly is not surprising.
