Remember when they deleted the entire site for a day and replaced it with some stupid Kid-Pets thingy? Or remember when they completely emptied some people's banks and sdbs? That definately went further than the news. And apparently they don't take plots seriously because they:
Drag Them Out
Give crappy prizes
Make the comics repetitive
Abandon some (a.k.a. kreludor...I was so smurf after I bought neocola tokens and got a battle set ready and then they said they were cancelling it)
As I said, I didn't remember any major April Fools Day stuff outside the news, but I'm not saying it hasn't happened.
As for what you say about plots, there are reasons for them being drawn out (so they're not all finished in the space of a week, and because there is more to do on the site than just updating plots). I also don't agree about the prizes - I actually happen to like all of the prizes I've gotten from plots, and don't find any of them crappy. I've also never seen a repetitive comic, and enjoy them all thoroughly.
And finally, I know everyone was so overjoyed at the thought of another stupid boring Dr Sloth plot (can't you tell I'm his hugest fan and was so greatly hanging out to see what would happen), but TNT obviously had their reasons for pulling the plot. It doesn't mean they weren't taking it seriously, or that they don't take any of their plots seriously.
Honestly, given the amount of work they generally put into their plots, I'd say that most of the time, they take the plots more seriously than the rest of the site.
Anyway, this is all just my opinion AND is now entirely off-topic and defensive over something that I didn't want to get defensive about. I mean, April Fools Day is meant to be fun... not something that causes arguments over whether or not TNT is taking this plot seriously.