Calm down guys--it's just another case of Yanks vs. the rest of the world. You're both right.
I must agree that Roy expresses the intuition of most of us Yanks that "with effect from" sounds weird to US ears. I may be a bit more used to it having lived in England for a while, but I've never heard it used here (doesn't mean you shouldn't use that translation!--I'm just validating Roy's comments about our usage, ok?).
But Rick, I'll bet my paycheck that although you're not British, you're definitely not American. You're gently chastising Roy with the count of internet hits didn't go far enough, because (I suspect) you were counting all references in English (or maybe even in all languages. But that doesn't tell us anything about usage in the US, if that's what you're interested in discovering.
Here's a way to take the measure of how widespread the usage in the US (can also be applied to any country of your choosing):
Count of all terms in the domain "us" (yes, there is such a domain!): 16 777 986
Count of "with effect from" in the domain "us":
Same trick, with say, Australia:
5,341 out of 11,977,591.
So, that should convince you that Roy's sense is an accurate reflection of US [non-] usage of this term.
Having said that, since continental translations are often based on British English, by all means go ahead and use "with effect from". Just don't expect it to be fully intelligible on this side of the pond.