Your success in summer courses will depend purely on your personality type. If you're an intensive crammer and you thrive off of pressure, like me, you should do well. I did four courses in summer overall, and got 2 Ds and 2 HDs.
If you're the kind of person with a more level and organised approach to study, the intensity of it is actually likely to freak you out. In short, forget being organised- in summer school its near impossible.
Here would be my summation:
Pros: get the course over with in a fraction of the time. Less detail/lower standard expected on assessments.
Cons: Intense- it sucks while you're doing it. Those on-campus sessions are all day, compulsory and lo-ong. Also, more expensive- and no HECS coverage. You will need to use FEE-HELP or pay full fee.
Hope that helps!