subl . should open MyProject.sublime-project if it is in the folder, else just open it as a regular folder

codeon.sh

#!/usr/bin/env zsh
# like workon from python virtualenvwrapper
# assumes that you have all your coding projects in ~/src

subl ~/src/*${1}*

subl.sh

#!/usr/bin/env zsh
# drop in replacement for the subl alias that will check first to see if there is a
# *.sublime-project file in the directory you trying to edit.
#
# setup:
#  `ln -s "/Applications/Sublime Text 2.app/Contents/SharedSupport/bin/subl" /usr/local/bin/subl2`

open $1/*.sublime-project(N) 2> /dev/null
[[ $? != 0 ]] && subl2 $1