Are Steam price cuts predictable?

If nothing else, you can be sure that if you pay attention and wait long enough, the game you so look forward to will be on sale eventually. I have yet to buy a game on Steam without a significant discount. I've had to wait quite a bit for some of them, but the vast majority will come on sale after a while.

It's common for them to discount GAME X in the run up/at the release of GAME X2. So, for example, expect the Fallout 3 pack to get a price drop pretty soon because New Vegas is due in October.

Short answer: no.

Slightly longer answer: price cuts Noooooo, sales yes. ie the Summer sale (no way to tell what tho) or discounts on iD games during QuakeCon

Because the discounts and prices are negotiated with the publishers, you'd be better off trying to analyse on the publisher level rather than across Steam as a whole.

Additionally, because people would put off buying a game if they knew it was going to be discounted shortly, Steam will most likely purposefully avoid any such pattern (to ensure maximum revenue).