I also have been using the higher end SPD's --- (XT and XTR level) for some time, --- I have cheaper SPD's, but the float and cleat engagement just feels better on the more expensive ones

Cons: They don't look very nice on a slick road bike, -- so I have procured a set of Dura Ace SPD's (7410 I think?) - they take the same cleat and shoe and are the same mechanism as the mtb pedals, but are single sided and have sleek looks that blend in nicely , even when used with Campy everywhere else