Hahahaha!
The pro-guilt community are working themselves up into paroxysms of joy, self-righteous anger and self-righteous justification over Knox's discussion on her blog of the April Fool's joke.
Let's add some proper perspective to this issue.
1. April Fool's pranks such as these are absolutely commonplace. The whole
point of such pranks is generally to cause temporary shock to the "victim", then to reveal the prank and laugh collectively at the deception.
Some years ago, I rang my mother on April Folol's Day and told her that I had just been told that I was imminently departing for Iraq (at that time just post-"liberation"

rolleyes

and rampant with civil war and attacks on westerners) to advise on reconstruction of communications infrastructure. She was temporarily in significant shock, and began telling me that I shouldn't go. I then - in traditional style - dropped the deception with "April Fool!". At that point - again, in traditional fashion - my mother's shock dissipated totally, and she laughed along with me and congratulated me on the quality of my April Fool's Joke.
In essence, this is exactly analogous to what Knox says she did in Seattle. She and some mutual friends made a house look like it had been burgled, so that when the other occupants came home, they were temporarily shocked by the apparent realisation that they had been burgled. I assume that it was at this point Knox and the other friends burst in saying "April Fool!" I wouldn't be at all surprised that the "victims" were laughing along with Knox and her friends once the prank had been revealed, and that they completely accepted their temporary shock for exactly what it was: the short-term intention of playing a decent April Fool's joke on someone.
2. Part of the nature of the original "rape prank" myth was that Knox and others had "entered the house" wearing ski masks (and, in some versions, carrying knives), in order to terrify the "victims". This is clearly a whole different order of magnitude different from the type of April Fool's joke Knox now describes. And that (in my opinion) is why Knox made particular mention that no costumes were worn: it wasn't a question of Knox (and others) trying to intimidate the "victims" - it was a question of Knox (and others) simply setting up a scenario (the burglary) to trick the "victims", with no threat of personal violence ever once implied.
3. In any case, whatever may or may not have happened in Seattle on that April Fool's Day is in no material way relevant to the trial. Trials are based purely on evidence that is specific to the direct circumstances of the crime being tried. Similar Fact evidence is only permissible under very specific circumstances, and only when it is directly relevant (e.g. it might be allowable to present evidence of a person's previous bad character if they were on trial for crimes that related to character).
Simply put, whatever happened in that prank (and by my reasoning, nothing malicious or comparable to the prosecution case in the Kercher trial happened anyhow), it's irrelevant in trying to assess Knox's guilt in the Kercher murder. It's also worth remembering that someone with (for example) two previous armed robbery convictions, who's currently on trial for another armed robbery, cannot have the evidence of the previous two convictions used against him in the current trial.
This whole thing is a massive non-issue in the context of assessing Knox's guilt - whether legal or factual - in the Kercher murder. It goes without saying that it's extremely surprising to see pro-guilt commentators who claim to be legal professionals saying that this is a massive game-changer. It's not.