At OLCI, you can choose any seat that's free. However, sometimes it seems they preassign seats for everyone since the seatmap may have only a handful of empty seats. Then again on some flights, the seat map is wide open (and the flight can still be packed).

Wkndtraveler, you mean that if I go to Manage My Booking 24 hours before T36, it allows seat selection without a charge (for a Silver)? Really? Worth a shot on my next shorthaul!