$ history | wc -l
  56201

I use a simple prompt_command hook to push my history (from all my machines) to a central MySQL database(https://github.com/fredsmith/history-db). Entries are de-duped and a tally is kept so I can do simple ad-hoc reporting:

  mysql> select * from history order by count DESC limit 10;
  +-------+---------------------+-----------+----------+-------+
  | id    | timestamp           | command   | hostname | count |
  +-------+---------------------+-----------+----------+-------+
  |     1 | 2015-09-02 19:41:45 | ls        | xicada   | 34458 |
  |    89 | 2015-09-02 14:58:33 | cd ..     | xicada   |  4332 |
  |   519 | 2015-08-24 18:38:55 | ll        | xicada   |  3229 |
  |     9 | 2015-09-02 12:37:05 | cd        | xicada   |  2250 |
  |    82 | 2015-08-28 18:27:07 | add       | xicada   |  1887 |
  |   329 | 2015-08-31 18:22:49 | gs        | xicada   |  1817 |
  |    48 | 2015-09-02 19:17:26 | git pull  | xicada   |  1696 |
  |   275 | 2015-08-24 18:23:44 | df -h     | xicada   |  1529 |
  | 15708 | 2013-10-08 01:33:33 | grid unn1 | Europa   |  1210 |
  |    44 | 2015-08-31 13:10:46 | git push  | xicada   |  1139 |
  +-------+---------------------+-----------+----------+-------+
  10 rows in set (0.02 sec)

It's pretty useful (I search through my history constantly with ctrl-R or using bash's history-search-backward hotkeys), and having a 56K line history file doesn't seem to impact history searching or shell startup any noticeable amount.