Our school only offers 2U and 3U maths acceleration. In our year there were 3 people [including me] who were accelerated in 3U and 2 who were accelerated in 2U -- although initially there were 7 people who were accelerated in 3U but people just kept dropping. I did my maths hsc last year [i'm in year 12 this year] and i have to say that it was the best thing because now i have 12 extra studies and it really does free up time. We all did really well in our results: in Extension - 1 person got an E4 and the other 2 got an E3; in 2unit - 2 of us got band 6, the others got high band 5s.
It was a little hard for us because we were only the 2nd year this was attempted [the year before us did it, but all except 1 person ended up repeating it anyway], so our school really had no idea what they were doing. We didn't have a teacher in years 7,8 or 9 and rather worked on our own -- although with no teacher telling us to do work, we pretty much bludged all maths lessons, which was fun, but i went into prelim work in year 10 knowing absolutely nothing, which made it really really hard and that's why so many people initially dropped.
And i think most of the girls in our grade thought of us as being "nerds" or whatever which was really hard on us. It didn't help that all the teachers made such a big deal about us being accelerated -- everyone was so sick of it all and started taking it out on us and taunting us. But it got better over the years and everyone really started supporting us and when we did our hsc everyone came to wish us luck and congratulate us when we got our results.
Sorry, i blabbed on a bit there.