My quest for the perfect grocery list continues. I've been using I Sync Tasks as described here. The author has been very responsive and the service updates the shared lists in about 60 seconds. It costs $1 per person per month.
In November Google updated it's Keep service with sharing. It syncs in real time for free. I lke the price.
There are good clients for the web and Android. iOS is notable by its absence.
Certainly Google will come out with an iOS client but in the mean time I started searching. I came across an article on GuidingTech. It referenced TurboNote for iOS and GoKeep for iOS.
When I tested TurboNote for iOS it would never complete logging in as others have noted in the reviews. It hasn't been updated since June 2014 so I'd avoid it.
GoKeep for iOS fared much better. The reviews that suggest that this is just the web presentation aren't completely correct. The body of the app is the web presentation but it is "wrapped." There are additional functions in the wrapping including an online/offline toggle and a slide-in bar on the left. This is where you can enable the zoom capability. Some reviews note that you aren't able to delete a note. This is because the note deletion function is in the drop-down of the "..." at the bottom of a note. As some other reviews mention this drop-down menu just blinks and goes away.
I found that it was easier to use the Google Keep web site on a non-iOS browser to set the various options and then use the iOS app.
GoKeep for iOS was updated late Novermber 2014.
To get a feel for GoKeep for iOS browse to http://keep.google.com in Safari. Incidentally the "..." drop-down doesn't work there either. If that looks good then install the free version. The paid version for $1.99 is actually a separate app so you'll want to uninstall the free version and then install the paid version.
There are still some downsides to Google Keep. I used the Google Tasks ability to have subordinate list items. Google Keep doesn't support this. I also used the "widget" capability of Google Tasks to present the list on the Google Mail and Google Calendar web pages. Hopefully Google will bring these capabilities to Google Keep in the future.