Yes before you all start I have done a search and know that judder is commone on many scoobs. However, it seems that the cure is often a STI replacement.
Trouble is my STI7 judders occasionally - only ever when cold, often after reversing.
Am I the only one or is it a 'feature' of STI's too?

 

No, not on your own, it affects all the range. only eradicated by replacement of flywheel. any other remedy will only work on a temporary basis.
The flywheel has high spots on its surface, so without removal for either replacment or resurfacing,judder will continue, simply only being noticable when cold, or in lengthy traffic cues.
So whilst in warranty, get it back to the dealer for a modified replacement.

 

Ta, I presume all dealers are aware of this and been happy to oblige?

 

I believe some dealers are "reluctant" to change flywheels, but ifany doubt from dealer, speak to Subaru Uk at West Brom, they will gladly "suggest" to the dealer the correct method of repair!