I ran across four April Fool's jokes this week, and only one of them did I immediately realize was an April's Fools joke.
ENWorld (
http://www.enworld.org/), a D&D site, claimed to be changing its focus to 1st edition, so that was the obvious one.
I think I was caught by Darths & Droids (
http://www.irregularwebcomic.net/darthsanddroids/episodes/0082.html) because on Tues morn, I was thinking the 1st was on Wed. I did think it was bizarre that Lucasfilm would be sending a cease & desist for that site when it so clearly falls under parody. (And Lucasfilm is generally online-fan-activity friendly).
Wookieepedia put its front page all in Aurabesh (fictional Star Wars alphabet). I just thought it was a stylistic change (there was a link to click to see it in English), and didn't think of it as a joke.
Today, I was listening to a Diggnation podcast, and they claimed that they'd been bought by Fox News. I didn't know which day's show I was listening to, and its clearly no longer the 1st, so I didn't think too much of it.
Maybe some of my non-wariness about April Fool's is that it wasn't a very big part of my life growing up. My grandmother died on April 1st, so my mother didn't enjoy April's Fools pranks. She didn't make a big deal of it, I just remember that once I did something (don't remember what - was probably more of a joke than a prank) on an April 1st, she told me that fact, and I never tried to do anything about the day since then.