I think everyone here's missing the vital part about 'supply and demand' - ie the supply part. Does everybody realise that from year to year, universities sometimes reduce or increase the intake for a specific course by hundreds? Say if Macquarie combined LLB increased its intake by 200, that may bump the course down by 0.5. However if Macquarie did so in its BIT (much smaller group), it may bump the course down by 5 points.
Obviously these are contrived examples, but it illustrates my point. It's impossible to discuss supply properly unless you're one of the few people at UAC or your university to know the plans for intake numbers. Very few universities disclose how many students are in a given course, and if they do, they're usually unreliable figures because they're later in the first year (after dropouts). Very few staff members at universities know about (care about, rather) the exact intake, either, because of people deferring, etc.
Secondly, I have no idea why people try to argue about the demand side of things, either, ie 'smartest group in a decade' blah blah. Some courses are in demand because they're timeless. Others, for example a lot at UWS, are in demand because they use buzzwords relevant to 18 year olds (forensics, criminology, etc). It's impossible to discuss demand properly unless you've done a bulk of empirical research. I personally would love to see research done in the area of HSC preferences, but to my knowledge, no significant work's been done. Most importantly, unless you know the trends of what kind of students (UAI-wise) apply for each course, and in what numbers, you can't make any predictions. Most people make assumptions based on 1) the current UAI itself, and 2) pretending that
x type of student (with their UAI) prefers
y kind of course; the second part of this has generally been proved to be flawed in the past, I think.
Since it's impossible to discuss supply and demand properly, there's really no way to properly gauge the jump or fall of a UAI cutoff for any given year.
This is not even getting into the issue of UAI 'tampering' (although it's not really the correct word) - where some universities seem to have lovely UAI cutoffs at 80, 85, 90, 95, etc.
So yeah, the bottom line is that you can't really predict these things at all, but rather you'll just have to work hard and hope for the best.
I don't see the argument that the cutoffs will affect preferences, either, if anyone wants to bring that up.
Late edit: At this point I'll add that the UAI system is fucked up, and itself creates another significant but unnecessary obstacle for students wanting to get into uni. I really hope that I see it go in my lifetime.