I found this last week and find it works quite well for me.
zipsigner.apk downloaded from market. It can sign an app or a complete zip if you made an update.zip.
Give it try if you want to sign things easier.
If there's a reason I shouldn't use it please let me know.
I tested what I signed so far on a few phones without issues.
d1 dx N1 [still messing with NS] also an older lowdef 3g fender.
For those of us out there that only change out png's on these apk's this works great for resigning it to make it installable still.