Alright, so here is the quiz I actually wanted to place online but couldn't. I just copy it from my notes - everyone who read what I posted in the "Predictions on HP 5" thread might know most of the answers.
Here we go!

!/ According to most of the fans, who will very likely fall in love?
a/ Harry and Cho
b/ Harry and Ginny
c/ Ron and Hermione
d/ Malfoy and Hermione

2/ There's a rumor about Remus Lupin having a brother. What might be his name?
a/ Apollo
b/ Romulus
c/ Castor
d/ Pollux

3/ Which character from book # 4 might later return as a teacher in Hogwarts?
a/ Fleur Delacour
b/ Viktor Krum
c/ Ludo Bagman
d/ Rita Skeeter

4/ What is said to be happening to Snape in book # 5 or 6?
a/ he will die
b/ he will return to Voldemort
c/ he will stop hating Harry
d/ he will fall in love

5/ JKR already said that something about _______ will be revealed in book 5. About whom?
a/ James Potter
b/ Lily Potter
c/ Molly Weasley
d/ Petunia Dursley

6/ Rumors say that something might happen to Percy. What?
a/ he will become a Death Eater
b/ he will become a minister
c/ he will die
d/ he will be exposed as an illegal Animagus and therefore be sent to Azkaban

7/ One of the Gryffindors might later become a teacher in Hogwarts. Who?
a/ Hermione
b/ Ron
c/ Neville
d/ Lavender

8/ Many fans suppose that the Dursley's neighbour, Mrs Figg, is actually Arabella Figg in disguise. But who is Arabella Figg?
a/ one of the "old fighters" against Voldemort
b/ a distant relative of the Potter's
c/ a retired Professor
d/ all of the above

9/ What could be another reason for Snape hating Harry as he does?
a/ he envies Harry
b/ he was in love with Lily Potter
c/ he despises harry for his relation with Muggles
d/ he fears that Harry could find out more about his past

10/ Which of the following rumors has so fas NEVER been mentioned?
a/ Dumbledore is Harry's great-great-grandfather
b/ all of these have been thought of
c/ Lily Potter was related to the Weasleys
d/ Aunt Petunia might turn out to be a witch, too

The answers come in the next post.

ANSWERS:

1/ => c. There are loads of hints in GoF - see how jealous Ron is when Hermione goes to the Yule Ball with Krum.
2/ => b. Romulus and Remus are characters from Roman mythology. They were brothers, raised by a wolf, and later they founded Rome. The only problem is that Romulus killed Remus...
3/ => a. This is not really my own theory, but it's worth thinking about. Fleur said that she would like to work in England to improve her English. I'm also sure that we'll meet Mademoiselle Delacour again, but I'd say she doesn't teach. Maybe she's helping Madam Pomfrey or so. Her looks could cure a lot of boys (or cause them to pretend to be ill just to get to the hospital wing... however!).
4/ => d. I can't remember where I heard that, but this rumor is very common. The question is: Who will be the lady? Professor Trelawney ?
5/ => b. That's a fact, JKR already stated it. She also said that in book 6, something HUGE about Lily will be revealed. No idea what this will be.
6/ => a. Percy read a book about how to seize power in CoS. I don't quite agree with this rumor, but I think the one who thought of it has a point there yet... sometimes, Percy is simply TOO keen on the rules. Of course it would be a real tragedy... but I wouldn't put it past JKR.
7/ => c. JKR already said that it won't be Hermione, and most of the fans think it will be Neville. He was good at Herbology, so why not? Also, this would mean that Neville isn't the one who is going to die...
8/ => a. Remus Lupin, Mundungus Fletcher, and Arabella Figg are the "old fighters" Sirius is told to fetch in the end of GoF. My theory on her is already posted in the "predictions" thread.
9/ => b. It makes sense, but I don't really agree on that.
10/ => b. Yup. And they are all quite plausible. Dumbledore being related to James Potter (and therefore to Harry, too) would explain e.g. why he offered to be the Potter's secret keeper (would he do this for any ex-student?!), and why he is the only person (apart from Harry) whom Voldemort could never defeat. Lily Potter, as often mentioned, had red hair - a fact automatically connected to the Weasley's. Maybe that's the huge thing which is going to be revealed about her. And as to Aunt Petunia - I don't want to repeat everything here, it's all been said in the "predictions" thread, too.

I hope you enjoyed this little quiz ... and don't hesitate to tell me what you think of it (but please be honest)! I love feedback

Thanks so much for all that, REALLY intrigued now and can't wait for the next one. Might have to read all the other again

I agree. That was just great. Now I have to dig out the books and do a little detective work myself. Thanks, Pearl.

It was great - and Lupetta think of the fun you'll have reading the books with Tinker!! Maybe by the time he's old enough to read them we'll all be out of our misery!!