I recently made my first contribution to ISFDB, and I have to say, it was a lot more painless than working for Wikipedia.
I'd happened out of passing curiosity to look up Damon Knight's critical-essay series, Monad, and discovered to my surprise that the third and last issue had no contents information. Well, I have all three issues, having subscribed at the time, so I registered myself with the site, used the previous issues' entries as a template, and entered the data, following the help entry's suggestion of adding a note reading "Working from book in hand."
Then I submitted it to the moderation queue, and within 24 hours it was up. Usually when I submit something useful to Wikipedia, within 24 hours some asshat editor has deleted it.
Also on ISFDB, when I egoscanned myself, I discovered, more to my horror than any other emotion, that somebody had entered the fanzine issue that my high-school SF club issued in my senior year. Now I have to decide whether to augment this info: correct the title, which they got wrong (it was deliberately confusing), link the co-editor to the entry under which he went on to write professionally under a different form of his name [he reads this: what do you think?], and - assuming I can dig out my copies from storage - enter the previous (which had a different title) and subsequent issues which they don't know about.