most of the above is very reasonable and correct advice.

SQ is (since aug-1-99) also miles&more partner of LH.

I would not/never use 50'000 (US) or 90'000 (LH) miles for a free transatlantic-ticket from Europe to the USA (in winter/spring, and after sep, you get eco return tickets to USA for DM 500 to 1'000 = $ 300 to 600 (may be you are then not at the very place you want to go in the US, but adding another 499 DM ($ 300) gives you supplemenetary 3 inner US-flight-segments to fly in North-America in the 60 days to follow your transatlantic flight (8 segements would cost 1'200 DM).

And with LH m&m you need only 25'000 miles for an one-way-transatlantic-segment-upgrade to business good on any eco-fare (with UA only 20'000 miles but not on any fare)- and on all flights (transatlantic and visit-US-pass) you win miles again.