Ermmm... Guys, be very careful on this. Yes you can book flights up to 31 March that can be taken within the maximum time of 11 months or a little more after that. But be very careful. If circumstances arise that you need to change any part of the trip you may have a very hard time. Star Alliance inventory is not going to be available to US agents to book after 31 March. There might be a grace period for ticketing or re-ticketing after that but that might be unofficial. For some airlines the ability to find or book or change Star Alliance award seats may unofficially disappear before that date.
You may say that's fine I won't want to change my booking. Hmm no you're still not safe. Have you any idea how many reschedules etc. there are by airlines in a whole year? Some of them are even reschedules due to daylight savings, that later (too late) switch back again. Your whole itinerary could come crashing down because the airline no longer has access to Star Alliance seats or Star Alliance award seats including a flight you might need to keep your itinerary together after a change not caused by you. There are already reports hinting that Lufthansa withdrew award seats from bookability by US Air. And in some parts of the world you may find you still need a LH flight to hold your itinerary together after schedule changes, for example. Good luck with you or any other airline trying to get LH to rebook your award seat in that circumstance. Even if the problem was caused by LH themselves, for example. There is also anecdotal evidence that in such circumstances TG can also be hard to get changes with and they change schedules and aircraft a lot.
Did US Air say they have arrangements for re-ticketing onto Oneworld flights? I really hope this works and for award seats. Would be better than the merger I went through. I had several complex award bookings that in the course of 11 months were completely trashed due to causes above in a similar situation. Good luck to anyone who books an award flight on Star Alliance by 31st March I will be watching this one and wishing everyone good luck.