Yep, roughly 10bhp and 10lb/ft, and you get improved throttle response. Costs £400 from AmD (it was only £199 when I had it done in 1998 - that's AmD rip off prices for you!)
It is expensive for what you get in terms of £ per bhp compared to turbo tuning, but I think it was worth it and would do it again.
If you are going for extra power - e.g. a cam - then you need it remapped anyway to make the most of the cam. May be possible to get cams and remap together by another garage for not much more than AmD charge for the remap alone.
I'm a bit out of touch with tuning on normally aspirated engines as almost everyone has jumped on the 1.8T or TDi bandwagon and those that remained - like TSR - went bust. I know that F2 Stu has spent a lot of time fettling his 16v unit (until it broke) - not sure who did the work on his.