yes curt: Lufthansa, Austrian, Lauda, Ansett (before going bankrupt), Air Canada, Singapore, Varig, SAS, Thai all were able to reserve specific seats on all StarCarriers (including on UA), for me.
UA (in FRA, or the european international desk in Ireland, or at any UA ticket office in North America) never gave me a positiv response to my requests for seat reservations on other Star-carriers (the only UA exception was the downtown UA office in Zurich, now closed).
[This message has been edited by Rudi (edited 10-08-2001).]