I have to state that i am a FI in the UK.
I did my PPL in the the states and really didn't understand the differences until I did my FI rating.
Its mainly to do with how the basics are taught and what your looking to do with the license afterwards.
In no way am I implying that USA trained PPL's are unsafe or not trained properly.
In the UK the whole method of flying is based on attitude flying and trimming correctly. In the US the instructors teach you to refer to your instruments alot more in the basic lessons.
Navigation in the UK is also done more by the numbers than in the states where track following isn't the sin as it is over here.
So you proberly won't notice anything until you start CPL and IR training where the FTO will be teaching you how the examiner wants to see it. This is when you might find yourself having to break some habits and relearn some methods.
Any thing else is based on what the airlines think.
If you can can get a JAR rated FI abroad who will teach you the JAR methods you should have no problem.
MJ