comics that did something:
Funny Farm did something in the style of early Peanuts strips, yet still managed to refer to Naziism
Sam and Fuzzy did a really strange "Sven and Fluffy" strip and a comment that I found hilarious (Sam and Fuzzy doesn't normally update on Thursdays, so add this to your reading schedule if you're a regular).
General Protection Fault took kind of the lame way out and printed today's not particularly funny or interesting comic with the text backward. Because, y'know, that's a "prank" or something.
Ozy and Millie referred to April Fool's Day, but didn't do a prank. It's kind of funny, but only if you know the personalities of the characters already.
WIGU did TWO comics (one without eyes and in strange colors), both of which feature Romy getting caught topless (no, you don't see anything, but it's still there)
Oh, and
Krazy Larry posted it's first strip in a year and a half. Still not sure if that's an AFD joke or a genuine appearance. Either way, it's funny.