at the risk of resurrecting a dead thread wanted to post this script I hacked together to find possibly orphaned packages. it checks installed packages against the original ROM list and for any dependencies.
for i in `opkg list-installed |sed 's/ - .*//'`; do if !(cat /rom/usr/lib/opkg/status |grep -q "Package: $i") && !(opkg whatdepends $i |grep -q "depends on $i"); then echo $i; fi; done