Hi Mark - thanks for your help. And on a Sunday, too :)
Following your advice, I found that when using a computed text field, the type is com.ibm.xsp.component.xp.XspOutputText
Checking the type hierarchy, this is a subclass of javax.faces.component.UIComponent
so a general solution to this problem is :
var v:javax.faces.component.UIComponent = this;
v.getId();
Which does the trick nicely.
Mind you, I do miss the old @ThisValue (just kidding :)
Cheers