Google's Punit Soni, who is responsible for the Plus mobile app, has said that almost all of the problems below will be solved soon. That's good news. In fact, Apple must be working with Google on the app's release because a first update appeared in the app store less than an hour after the app became available. (Apparently an old version intended for testing was what got pushed live at first.) That update freezes when you try to load it, but if you force close it once it will work the next time.

Problems unique to this app.

• Plus is only available in the US iTunes store, international users appear to be out of luck. That might change as the roll-out continues. Update: Sure enough, some UK and Canadian users report that they are able to download the app now. Great news!
• The Plus app doesn't work on the iPod touch, inexplicably.
• IPad users are out of luck, you can't even use the iPhone version and expand it.
• The app is crashy on iOS4, and super crashy on iOS5 betas.

More general issues with the mobile Plus in general.

• Push notifications are cool - but more granular control over them would be nice.
• Photo uploading on iPhone is good - but it's not automatic like it is for Android. That's just how it goes.
• You can't reshare posts.
• You can't like comments.
• You can't see who liked things.
• You can't invoke peoples' usernames with Mentions.

Those are all very frustrating features to be missing across the Plus mobile experience. Hopefully the whole thing will be improved promptly so that Plus on mobile can be as remarkably compelling as Plus on the desktop.

I'm on Google Plus here.