Of the US pro-conti or conti level riders that I have seen race I would say that Ben Jacques-Maynes would make a very good racer in one day races (Het Nieuwsbladd, Gent-Wevelgem) or short flattish stage races with a time trial of no greater than 20km that decides the overall (3 Days of de Panne, Criterium International, 4 days of Dunkirk etc.). Other than those he would make a good domestique for other races and potential stage winner in breaks. With regards to the other racers.
I don't yet think they are ready to set themselves up in Europe as the style of racing as well as the disatnces would see them struggle for 12-18 months which may see their potential destroyed unless they were in say Columbia-HTC or Garmin-Slipstream.
Now as these two teams require results during the season, both require really good riders in their squad throughout the roster. This leaves maybe one or two spaces for the younger up and coming riders. I think we all know that Columbia-HTC looks at the best talent in Europe as these riders and Garmin tries to take the rest from Europe and USA. But, again I see Garmin as being more inclined to take a European as they would have a "harder" racing background.
Its a terrible thing to say as it will only diminish the US proportion in the higher echelons of the sport in the future but it is what will occur if its not addressed.
In a couple of years though I think Taylor Phinney will realise his talent and become a major force in European racing but it will need more with his talent to get into the ProTour level.