I must admit, I hadn't thought much of this power till I took a look at this and realised that at higher psy ratings it basically allows you to move enemies wherever you **** well please. However, further thought has prompted me to ask whether the rapid push is always 'away' from the caster (the exact words are 'thrown backwards') or whether the angle of push can be chosen by the caster, allowing for effective 'pulls' or, possibly even more gamebreaking, launches into the air. Any thoughts?

While I believe the intent is to be push away only, I've always ruled it as being lateral movement, in gravity.

So both push and "pull".

In zero g it can be in any "direction".

I would interpret it as a throw in the immediate direction of away from the psyker. Pretty much how the power "Mass Force" works in the Skyrim mod pack of spells:

http://www.nexusmods.com/skyrim/mods/19270

It's just a giant "Sod off". If you wanted to pull towards you or lift, that would arguably be what you might want Constant Motion for, lifting them up only to drop them from a great height.