Of course, this always use the effectiveness of zealot bombing and DT harrass.
To put it simple, this can be used in late game when you know your opponent has an eco advantage. The way I've seen it, the oracle range is very limited and doesn't get all the minerals in a patch and (as far as I know) doesn't stop gas production. So this usually involves around these:
2 oracles per opponent base
1 warp prism per 2 bases
5 or more warpgates
This is only a strat that can be used in late game.
Use entomb to close all mineral fields. There is no warning system for this and keep it hidden and fly only around the mineral fields, but out of sight and range.
Once your opponent realizes that you are hitting the eco, see where his main army is going. If it gets near any of your bases or main army, STOP THIS BUILD RIGHT NOW!!! If it stays put or tries to find your oracles, keep using this build. Zealot bomb his mineral line as soon as you put down your entomb.
Oracle's abilities also help out on the battlefield as well. If the opponent is trying to attack your army, you can use Phase Shift to make units (such as the colossus) form attacking and using abilities. Use Pre-Ordain to find out what your opponent is working on before hand in early game. (1 should do in early game)
Depending on the supply it costs, its not a very bad build. If you don't mind building stargates early, or late game.
All of my info is from Blizzcon and this link:
I'm open to any different strats with the oracle.