I had a great time! I learned some stuff, made some great friends and did very well academically allowing me to get into the university and program I wanted to (Waterloo Nanotechnology Engineering).
Some tips from someone who just finished high school:
-Always do all of your homework, once you get into this habit it goes quickly most of the time, and if you slack off in 9 and 10 thinking they don't matter, the chances are you will slack off in 11 and 12.
-For the love of god have fun! If you do nothing but school you will burn out, I had a hard push at the end of 12 because I missed enough classes to put me behind because of illness. At the end of that sleep deprived study spree I was indifferent to the outcome of my year and almost gave up, I burned out.
-Connect with your teachers. If you stay that extra minute (if you have the time) after class and talk to them; ask about, tell them about something related to the class from the news, just anything really. They will like you more as a student, and will give you a break on some occasions, sometimes not overtly, and you will enjoy class more knowing your teacher as a person.
-Sleep regularly. The most mark destroying force besides being unprepared is fatigue. My marks on tests that I stayed up late studying for were noticeably lower than the ones I slept well before, and trust me caffeine does not help that much.
-Finally choose a good peer group. My group was diverse, and fairly large, but not all of those people were good friends, just at school buddies. Talk to people and be a good person and people will notice. That is not to say everyone will like you, but as long as they respect you, you will be well off. Remember, there are group assignments in high school, and having a network of people you can sort-of trust helps.