Hiya!
Remember to get your tax status reviewed for any rental income you may acheive in either the US or UK home. Prices in the USA for homes has always been much more affordable like for like/price wise and so makes for a good investment/2nd home location for many UK/USA based individuals. The double taxation treaty is a welcome agreement so that you don't pay tax twice. Figure in costs for a good tax accountant familar with both systems (only have to look as far as Guya and Lizzit on the tax section here!) and factor in costs of looking after the 2nd property.
The good thing with the USA is that laws, practices, transparency and rules & regulations all combine to make for a potentially safe route to ownership whilst your in the UK or vice versa. As always, due diligence is required!
I've found that 15% for full management is a common figure given on both sides of the Atlantic for property management services. Some places I think charge more so check out what you get for the extra outlay.
Lastly, as the thread is saying own a house in the UK and America, I've assumed one place would be rented whilst occupying the other - it may well be that certain people can and will choose not to rent out the other property and simply maintain it just for their own use or immediate family etc. Still worth taking tax advice though just to cover all bases.
Snownrs - With careful planning and evaluation of your own personal situation and aspirations, it's perfectly normal to go the route you've thought about, I know quite a few people who do this to one extent and another and it's very common. Just the usual 'do your own research' applies and try not to get too carried away with the currently low property prices, but instead look at the complete ownership picture to suit you and your family's scenario.
Cheers! DtM! West London & Slough UK!