There's not yet a service that shows a public timeline based on the ofirehose.com data. It would be nice if someone would create it; otherwise I will. Groups are actually baked in and you can get to them through the API, but not through the Web interface. I want to get what's visible stable and working first. I absolutely think that friend-finder stuff is a good idea; if you have a StatusNet site pump2status.net should give you an idea of how this will work. Similar bridges are going to happen for Google+, Facebook, and Twitter. Tag-following doesn't exist in pump.io and probably never will, but someone could make a service to do it based on the firehose data.