of course it invalidates your warrenty :
just a risk you have to take if your turbo blows up .... VW wont touch it cuase its been boosting above the spec they set out but again .. they have to find out you have it chipped to do that.
It wouldnt invalidate anything except your engine / turbo for example if your cup holder breaks... they can't say it's cause your car is chipped.
But if the faults directly related to the mod... ur up sh*t creak with no paddle.
mines been chipped now for about 8,000 miles ... got it done in march i think no problems.. have decided i need to get better disks and pads tho - but yea i love it. it's more than worth doing.
in the UK you can get your re-map done by www.mega4.co.uk
there are 2 Revo's stages.. stage 1 standard car - just the chip .. stage 2 is a remap of stage one for allowances if you've added say a turbo back , downpipe new back box, induction kit.. and anything else really.
stage 2 - not really an option on a standard GTI but any "stage" is way better than stock!