Couldn't find another thread about this.

I'd like to know other people's experience of always getting upgraded being a Star Alliance Gold (Eurobonus Gold/Diamond) with different Star Alliance airlines.

The only one so far I've found out is a guaranteed upgrade from Economy to Economy Extra (Or plus, or whatever it's called) on United flights. It is subject to availability of course, but you can request it directly after booking via their Customer Service.

Any other airline where you've had the same experience?