Our HBase cluster (3 boxes serving 30 human oracles, each submitting data at a rate of 1 record every 5-10 seconds) choked frequently - i.e., it stopped accepting new records. Ultimately what I had to do is have the human data go into postgres and a cron job flushed that into HBase every half hour or so.
I'll emphasize that this is probably my fault. I'm not claiming HBase doesn't scale to 30 concurrent users - clearly Facebook demonstrates it can. But I couldn't figure out how to make that happen. HBase is a complex system and I make no claim of understanding it.
ElephantDB + MaryJane are simple. There is almost nothing that can go wrong - put together they probably amount to 5000 lines of code and have as many as 10 minimally interacting configuration options. The effort required to manage them is minimal - I had EDB working flawlessly in less than a day.
HBase is an enterprise tool. It works well if you are Facebook and can put a couple of people on maintenance duty. It's overkill if you are Styloot (my stealth mode startup, currently smaller than Backtype).