Search the forum mate for reliabilty threads as it's been done to death but the 1.8T engine is pretty much bullet proof. As long as it's been serviced correctly then it should be fine. The earlier turbos have been known to fail, but it is a bit of pot luck as some cars fail and others don't. The later model, 2001 on roughly, had the K03S turbo and drive by wire, and these are the better engines.
Mine has been mapped for a year and no problems with it and the same can be said I think for all the 1.8T's that have been mapped by R-Tech....