From my experience, Star Alliance is anything but seamless! Concerning the partners that I have flown:


Air NZ-Good Airline, Seems to understand the Alliance better than others, AKL-CNS flight was cancelled once, gave me an upgrade from coach to business/first and free night in AKL due to 100K level (on a discounted fare!).
Ansett-Good airline for coach travel in Oz!, Getting miles posted is like pulling teeth from a rhino! Stay away from domestic business class!
Lufthansa-I have always had a soft spot for this airline, logged over 300,000 miles during the 80's from the MIA-FRA-JNB, MIA-FRA-MRU routes. Have not flown recently, although I suspect they are on of the better Star partners.
Thai-Avoid at all costs, Inter-asian flights are tedious, no recognition for being a Star Gold!
United-Solid Mileage accounting, 100K level keeps me ahead of the pack. Decent E-tickets as long as NO code-sharing is involved!
Varig-Does not seem to know what the term "alliance" means! Went 3 rounds with Mp to get miles posted.

The only benefit I see now is the ability to gain miles for FF elite levels from all partners, but one has to be very alert regarding their MP statements. Lounge access helps only rarely.


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Getting Closer to The Million Mile Dream!