Not too long ago I complaint about the lack of a groceries list apps on iOS and why no one really fills the niche with a thought-thru product.
Of course, I was clear that I could use OmniFocus for it, but decided not to for various reason. Jonathan Poritsky uses OmniFocus extensively to do his groceries and has written a very detailed post about it.
He deploys all the good tricks you know about to make it as efficient and nice as possible: Project templates, find project with AppleScript, contexts and even a custom perspective icon. Really worth a read.