Thanks for all the comments so far- it looks like the Android Market is having some issues
Crap. Murphy's layin the smack down with his law again.
To answer the questions:
It's only USGS Stations at the moment. USGS has a uniform web service for getting data from everywhere in the US, so it was the path of least resistance to build an app using that service. As far as I can tell, there's not a lot of difference between DWR data and USGS data, but I haven't looked at it that closely.
I am considering using data from NOAA's AHPS services
in order to display forecasts and flow stages, etc.
As for the difficulty in finding a gauge, did the onscreen keyboard show up when you arrived on the site listing page? It should, but if it doesn't you can make it appear by holding down the menu button. You can then filter by site name.
I have thought about an alarm capability- however, before I write that I want to build the ability to regularly reload favorites in the background so they will still display relatively up-to-date data even if you lost cell reception hours ago. With that in place, it should be easy to add alerts.