This board is so interesting... maybe i am just too self-involved 
Anyway I'm a Y5 in NUSHS, and everywhere I go to, be it for external courses or to external labs for research, there are people who'll ask me what NUSHS is like... Most of the time, I direct them to Kiasuparents (since it's so fascinating here) 
I thought I might as well share some of my experiences with you guys here, which is a far more productive thing to do than to play computer games.
Hmm here's a disclaimer first: I joined in '06, and many things have changed since then, so what I'm typing here may not apply to potential NUSHS students.
1. The Entrance Test
Don't mug too seriously for it. If you get into the school by studying really hard, you're going to have problems surviving here, especially in the later years. Y1 and 2 were simple though. If you truly love math and science, you should have some prior knowledge already anyway... A lot of the questions aren't PSLE-style anyway. The main objective in this test is likely to be to check if you think. That's why the test can be quite tough. It isn't necessary to get everything correct... For me, I know very well that I got A LOT of questions wrong/didn't know how to do. But I still got in, and was the only one from my pri school to do so even though my results for math and science paled in comparison to my languages in pri sch.
Right now, I have an average CAP of 4.5 although I slack a lot (as I do presently), which is quite easily obtainable anyway due to CAP inflation.
2. The Camp
Congrats! Second Stage. Aaaah, this camp requires a lot of common sense. Not just in handling lab work/essay test/other academic stuff, but in cooperating with others as well. Participants of the camp are usually separated into small groups, which are led by NUSHS students. These NUSHS students have no power whatsoever to influence your entrance into the school; we're merely here to make sure you stay safe and don't get lost.... Unless you're behaving really erratically such that a teacher asks us for our opinion. Oh yea, taking the initiative during the camp will score you a LOT of points. You have to sort of take the lead, but make sure you give others chances to show their capabilities as well. Being quiet just makes it difficult for the teacher to assess your performance.
3. In the School
Congrats again! Final Stage. Make sure you mug hard from now on, unless you're a real genius like Douglas, Junle, Clemen etc who joined NUS in Y4 because they're just too clever.
Try to spam electives and enrichment in Y1 if you think you can handle it, because they're really fun during the foundation years. The variety of electives gradually dwindle over the years. Oh, and if you're thinking of taking a 3rd language... think again. It can get quite taxing, and most of the time you'll have to stay till quite late in school (due to timetabling problems).
I've pretty much sailed through my 4.5 years here without much problems even though I was from a very neighborhood pri school. The teachers are very approachable and will always help you. I've never met a teacher who was reluctant to help.
For me, the languages eventually got tough. I used to score As for English, but after all these years, my As have transposed to my sciences. By the way, I think NUSHS students mostly have sucky presentation skills compared to other schools like VJC or RJC even though we have presentations every other week or so.
Another dumb thing about NUSHS is that we change teachers pretty often. I think MOE sends some teachers here to learn the ropes and then takes them back to be distributed to other schools. The number of teachers who have left the school since '06 can't be counted on both hands and feet. The infusion of new teachers is very rapid too as well.
But the non-MOE, graduates fresh from NUS/NTU teachers are fantastic -- and they don't go away for a long while! ^^ Every math and science teacher here really know what they're teaching.
What else...
Yea! How could I forget about this? Hostel life is awesome in NUS High I'm glad it's compulsory for Y5.
And our school orchestra (NOT BAND!!!) is led by the most fabulous Dr E Wong!
We have exchange programmes too! And I love the events like SIMC that NUSHS organizes. The interaction with overseas participants is really good. And some Y6 went for overseas CIP that was self-organized this year. Our school encourages more local service learning projects than overseas, in my opinion. But it's true we dont need to go overseas to help other people 
Haha. I think that's all~
I'll gladly answer any questions (if I remember to return to this board) and good luck.
edit: i forgot to mention.. We have very little homework. like seriously, super little compared to other schools. The grading system is tilted in our favor (60%CA40%Exam) which essentially makes it near impossible to fail a module, unless you don't touch any of the assigned work. Even if you fail, you can take some sort of a retest (not too sure because I've never done so -.-). And rejoice, because there's no holiday homework (most of the time)!!
wah this post is super long...
anyway i just saw this on some page of this forum
\"Those year 5s who said they are slack, let them take a few honours, olympiad training, and a good ARP before they dare to say they are slack.\"
I take Bio Hon, Chem Hon, Phy, Math, Bio O, have a very demanding ARP =.= and take part in SYF... But I still feel that I am slacker than people from other schools who have to spend a lot of time on homework.