I have noticed recently that when I post a new item, the post times are 3 hours behind. I finally decided to check this out, and browsed to Control Panel >> Administration >> Settings >> Date / Time Settings.
When I had gone through the settings after upgrading the server, I saw this box for Time Zone. I live in West Chester, PA, which is in the Eastern US time zone, so that's what I selected.
Tonight upon further inspection, the little help tag said it should be set to the time zone that the database server resides in.
Fortunately, Community Server appears to process dates according to UTC, and this change filtered out to all of the posts, which now display the correct times.
Doh!