Bash/shell scripts aren't working on Ubuntu

I was just writing a shell script - it all worked fine on the command line so I put it in a file and ran it:

% sh myscript.sh

But it generated an error - specifically I was trying to use brace expansion (a Bash only feature) which it now didn't seem to like. What the heck?

It turns out that on Ubuntu they have switched to a faster-simpler default shell (/bin/dash) - which does actually help to improve boot times - but is no longer bash compliant (so no fancy features - just POSIX 1003.2 features only). So what's happening is that my script is being run by dash - despite it the fact it starts with the usual #!/bin/bash - which confused the hell out of me. Anyway watch out if you've got lazy old habits like assuming that sh is bash.