It does induce a geeky joy but it's ephemeral for the most part as Google is vastly superior in usefulness. I learned about units few years back, used it for a while, and I can't even remember when but I just started Googling the conversions instead of switching to the terminal window.
I mostly use Spotlight (on OS X) to do conversions since it saves me switching to the browser or terminal. It doesn't handle as advanced conversions as Google does but it handles 90% of my common cases (including currencies)
user@server:~$ units -V
GNU Units version 2.11
with readline, with utf8, locale en_US
Units data file is '/usr/share/units/definitions.units'
Personal units data file is '/home/user/.units'
(file does not exist)
Copyright (C) 2014 Free Software Foundation, Inc.
GNU Units comes with ABSOLUTELY NO WARRANTY.
You may redistribute copies of GNU Units
under the terms of the GNU General Public License.
user@server:~$ units
Currency exchange rates from www.timegenie.com on 2014-04-02
2866 units, 109 prefixes, 79 nonlinear units
You have: 3millilightseconds
You want: miles
* 558.84719
/ 0.0017893979
You have:
user@server:~$