Using @vojtajina's script as a starting point, I tweaked it until I came up with something that works well for me. I thought I'd share it just in case someone else might find it useful.
if -z $@ ]; then
# no arguments, let's just open sublime
elif $1 != '.' ]; then
# passing args and $1 is not a .
# look for a project file ... redirect stderr to /dev/null so
# we won't see the error message if the file does not exist.
# changed this from `find . -iname *.sublime-project` because
# that does a recursive find which is problematic when wanting
# to open something like a home directory (recursively looks
# for all sublime projects ... not good). this also assumes
# there will at most one project file in a directory. not sure
# why someone might have more, but if they do, they should
# specify on the command line which one they want to open
PROJECT=`ls *.sublime-project 2>/dev/null`
# added quotes around $PROJECT to account for spaces and such
# in the file name
if -e "$PROJECT" ]; then
# project exists in current folder, open it
sublime . --project "$PROJECT"
# no project, open current folder
1) This script works on Mac OS X 10.7.4. I make not guarantees it will work unmodified anywhere else.
2) This script depends on a symlink in your path as such:
sublime -> /Applications/Sublime Text 2.app/Contents/SharedSupport/bin/subl