I'm not sure about this "working the engine harder" business. I'm not particularly technical, but my understanding is the remap actually makes the engine more efficient.
Therefore the engine actually has to work less to achieve the same performance as stock, this is why some owners experience improved fuel economy e.g. if at standard the engine sits at 3,000rpm at motorway speeds, after a remap it may sit at 2,900rpm - therefore less stress on the engine and less fuel used.
The above of course is my opinion, based on what i've read here, I would like the opinions of chipped A3/S3 owners. Btw i've not read any reports on here of dissatisfaction with the reliability of chipped Audi's, certainly nothing that can be attributed to the remap.
I don't have a chipped car as I am waiting for a solution that can be switched between stock and remapped without c/control and is COMPLETELY undetectable (that could be a bit much to ask). AMD OneClick would have been ideal as it also could have been posted to me.
One final note is that the issue of warranty seems to be particular to the dealer. Although they theoretically should act as Cebrey said and only reject claims attributed directly to the chip, some can be awkward around this and really put you through the ringer.
You may be lucky most dealers won't even check or notice a remap, at the end of the day they get paid by Audi for warranty work, and few really care.
Unfortunately my dealer told a colleague of mine if he puts his Miltek on his V8 S4, he'll invalidate his warranty. What a bunch of nobs. /ubbthreads/images/graemlins/burningmad.gif