I find it hard to keep up with the Communities when mobile. Usually when I am in front of a computer I have “work” to do. Those times when I have the opportunity to interact is usually when I am mobile (i.e. using Android between meetings, waiting at the airport, standing in line for a rollercoaster, etc.). Having an effective mobility platform is pretty much standard for any successful social media platform.
Using the web UI with a mobile browser is slow on 3G as well as the layout is not well suited for a small screen.
Email is an option… receiving emails and replying to Communities emails works but isn't optimal (and honestly have I given up on this method). We all receive enough emails; it seems excessive to be forced to receive emails just to interact while mobile. On top of that there is only one email client (iOS) that can group the emails from a thread which makes the inbox clutter even worse by not being able to collapse threads.
I find the My Stuff URL very useful when using a full browser to keep track of updates. Being able to follow and quickly see updates to the discussions I am active in should be this easy with a mobile app.