We just ran into this again today, where we forgot to set scanner caching and observed bad performance.
The default of 1 does not seem to make any sense (except for very specific case of large/wide rows).
Any value between 10 and 1000 should be OK, really. Maybe the default should be 100.
This would also go some way to avoid the perception that HBase is slow for folks who are just playing around with it.