I have contributed to Wikipedia through technology articles and wikibooks, and occasionally about things I am studying though I do not think it substantially improved my comprehension of those topics.
I have also several times contributed things that has rightfully been reverted by other editors, so despite my many contributions, I understand both sides of the proverbial coin.
Lately, I have been very interested in using Wikipedia to determine the legitimacy of companies or phenomenons. Sometimes it works, sometimes it doesn't.