You need to book a non-refundable flight for the Silver status to take effect. I found a one-way flight from PIT to LGA on 07/14 for $43+tax=$54. Can you find cheaper?
With Star Alliance Silver you and all companions booked on your itinerary will get 2 free bags when you fly on Star Alliance carriers like Continental, United, or USAirways. You may also get upgrades on USAirways and people have reported being able to get Economy Plus seating at the airport when flying United.
With bag fees as high as they are these days it can be worth doing this just for the free bags for an upcoming trip!
-Allow one to seven days for Silver Preferred trial status to take effect following ticket purchase date.
-Silver Preferred trial status will be valid for 90 days
-Only tickets purchased at usairways.com will qualify
-The last date to register and purchase a qualifying ticket is August 15, 2010; travel must begin by Sept 15, 2010.
-If you’ve done an elite match or trial elite status with USAirways within the last 24 months you will not qualify for this program.