For all practical purposes (except a clock) the 10 Hz difference between 50 and 60 cycles don't matter.
I'm not quite sure what kind of adapters you're talking about. Also, be adviced that there are different kinds of European plugs/outlets.
This one
[img]http://www.holzinger.cc/unterricht/eurost.jpg[/img]
being the most common one.
Normal European current is 220V/50 Hz, but you'll find 230/60, too. This difference is neglibible.
Highpowered appliances, like ovens, boilers, stationary saws will run at 350/50.
Where was I?
Ah yes.
Some devices, like computer power supplies can be switched between 115/230. For the rest, you'll need an adapter, usually to be had at RadioShack or thereabouts. If they only have adapters to use US appliances abroad, get an adapter to use Euro thingies in the US from www.ebay.co.uk. or www.ebay.de.