Running this script:

#!/bin/sh

function echo {
  /bin/echo `date` $*
}

function foo {
  echo START foo
  sleep 5
  echo END foo
}

echo "start script"
foo &
echo "called foo"
sleep 10
echo "ended script"

gave this output:

Wed Apr 29 13:31:30 EDT 2009 start script
Wed Apr 29 13:31:30 EDT 2009 START foo
Wed Apr 29 13:31:30 EDT 2009 called foo
Wed Apr 29 13:31:35 EDT 2009 END foo
Wed Apr 29 13:31:40 EDT 2009 ended script

which is exactly what I would have expected. Delays in the right place and so on.

So, this means that you can do multithreaded programming in bash!

The only caveat I see so far is that the script ends when the main theread ends. Thus, the sleep 10 was needed to allow the 'child thread' enough time to run.