As someone who myself began my training in the UK and finished in the states I would say,
The standard of airmanship taught in the UK is far higher at all the clubs I've been to.
The R/T is far briefer in the US and may make an US qualified pilot feel a little overloaded when he returns.
The UK standard of instruction is generally better.
I believe that a fear of flying in anything other than a clear blue sky may be engendered.
However,
I had reached 30+ hours when I decided to go to the states. I had probably had that many hours again cancelled due to the met. So whilst I would have loved to have completed in the UK I couldn't afford anymore TIME.
The US make GA as easy as possible - cheap fuel, friendly ATC and no landing fees, whilst it sometimes seems that the UK goes out of its way to make light aircraft unwelcome - high prices, busy airports which sometimes make GA unwelcome.
So to summarise I would recommend that people reach at least solo standard before venturing to the states (Solo standard can be reached quite quickly without requiring to much from the weather). This will hopefully give you a good sense of airmanship - not to mention enough wisdom to treat any dodgy advice with a pinch of salt!
Gaz